vm: test uses thread-unsafe _page_free()

[niewim19]

Inside the following test:phoenix-rtos-kernel/test/vm.c:test_vm_alloc() unlocked version of page deallocation function _page_free() is used.
Here: https://github.com/phoenix-rtos/phoenix-rtos-kernel/blob/509945e05ee1da4c22bde4ec1833007c17711306/test/vm.c#L53

Inside this test's body, page was allocated using locked allocation function. Is it then necessary to deallocate it using unlocked one? This is the only usage of _page_free() outside of phoenix-rtos-kernel/vm/page.c which seems as the only reason _page_free() is not made static. And as there already is locked version of page deallocation phoenix-rtos-kernel/vm/page.c:vm_pageFree() (https://github.com/phoenix-rtos/phoenix-rtos-kernel/blob/509945e05ee1da4c22bde4ec1833007c17711306/vm/page.c#L153C28-L159) it would seem reasonable to:

• use locked page deallocation function in test body
• made phoenix-rtos-kernel/vm/page.c:_page_free() static
• adhere to naming convention with the following change: _page_free() -> _pageFree()

Note: this issue is also mirrored in nommu version of page module: phoenix-rtos-kernel/vm/page-nommu.c