Enable building the GCC Cortex-R5 port without an FPU (#586)

* Ensure configUSE_TASK_FPU_SUPPORT option is set correctly

If one does enable the FPU of the Cortex-R5 processor, then the GCC
compiler will define the macro __ARM_FP. This can be used to ensure,
that the configUSE_TASK_FPU_SUPPORT is set accordingly.

* Enable the implementation of vPortTaskUsesFPU only if configUSE_TASK_FPU_SUPPORT is set to 1

* Remove error case in pxPortInitialiseStack

The case of configUSE_TASK_FPU_SUPPORT is 0 is now handled

* Enable access to FPU registers only if FPU is enabled

* Make minor formating changes

* Format ARM Cortex-R5 port

* Address review comments from @ChristosZosi

* Minor code review suggestions

Signed-off-by: Gaurav Aggarwal <[email protected]>

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Signed-off-by: Gaurav Aggarwal <[email protected]>
Co-authored-by: Christos Zosimidis <[email protected]>
Co-authored-by: Gaurav-Aggarwal-AWS <[email protected]>
Co-authored-by: Gaurav Aggarwal <[email protected]>