PX4/NuttX branch test: master

NuttX:
 - https://github.com/PX4-NuttX/nuttx/tree/master
 - PX4/NuttX@82b276a

Changes from PX4/NuttX (PX4/NuttX@1f2f6d8) in current PX4/master (6672284)
PX4/NuttX@1f2f6d8...82b276a

82b276a (HEAD, origin/master) binfmt/nxflat.c:  Trivial design simplification.
622202d binfmt/nxflat.c: Update to last NxFLAT change:  The logic must respect the reference count before freeing the dspace memory region.
ba8714d binfmt/nxflat.c:  Correct a double free debug assertion.  This occurs when groups are enabled:  (1) once via binfmt_exit and unload_module, and (2) once via sched_releasetcb().  this was corrected by adding logic to free/unload the memory once and nullify the pointer so that cannot be freed a second time.  This commit resolves Bitbucket issue #145.
043df95 arch/arm/include/nrf52/ and arch/arm/src/nrf52:  1. Added 52840 family support 2. Use common irq and memory layout header file for 52832 & 52840.
f6b00e1 tools/nxstyle.c:  Fix logic error that prevent detecion of '/' and '/=' as operators.  net/:  Minor updates resulting from testing tools/nxstyle.
0a7f764 Merged in raiden00/nuttx_h7 (pull request #839)
db2310b lib_gethostbyaddrr.c edited online with Bitbucket
f33ed3c *Merged in zhoukejun/nuttx_nucleo-f767zi (pull request #838)
20e7ee5 configs/omnibusf4/README.txt:  Update README.
aa4f7c9 graphics/nxmu/nxmu_start.c:  Extend nxmu_start so that receives a display number as an argument.  This makes it possible to have multiple instances of the NX server running on boards that support multiple displays.  Also includes updates to boardctl() to accept display number paramters.

Apps:
 - https://github.com/PX4/NuttX-apps/tree/master
 - PX4/NuttX-apps@520bd6a

Changes from PX4/NuttX-apps (PX4/NuttX-apps@7db2a35) in current PX4/master (6672284)
PX4/NuttX-apps@7db2a35...520bd6a

520bd6a (HEAD -> master, origin/master) Merged in zhoukejun/apps_nucleo_f767zi (pull request #171)
e063e93 apps/examples/nxterm:  NxWM passed the size of the NxTK sub-window but nxterm example passed the size of the complete NxTK window.  They must be made consistent.
66af5b4 apps/Nxwidgets:  Fix some recently introduced errors found in build testing.
e4e00f7 apps/examples/sx127x_demo/Kconfig:  Fix misplaced 'if'
c019c9d apps/examples/modbusmaster/mbmaster_main.c:  eMBMasterRegHoldingCB cannot be static.
53e6f4b apps/examples/nxterm, graphics/NxWidgets:  Replace illegal direct calls to nxterm_redraw() and nxterm_kbdin() with new boardctl() calls.
6529a84 apps/examples/nxterm:  Most configuration options were not available in the Kconfig file.
c341abf graphics/NxWidgets/nxwm/src/cnxterm.cxx:  Part of the last change was still in he editor.
061b433 apps/examples/nxterm and graphics/NxWidgets/nxwm:  Replace direct calls to nxtk_register with legal, indirect calls via boardctrl(BOARDIOC_NXTERM).  Replace calls to (deleted) nxterm_unregister().  The correc way to delete a driver is by unlink'ing it.
2eaf2e0 (origin/px4_firmware_nuttx-7.28+_rt) aps/system/cu/Kconfig:  CU term depends on TERMIOS and should select it.