fwk: Remove dependency on RTX threads
The multithreaded implementation of the framework currently depends directly on Keil RTX because it directly allocates the thread control block itself.
This change instead replaces RTX's memory allocator with the framework's memory allocator in a way that RTX can now allocate its own threads through the generic CMSIS-RTOS interface.
Change-Id: Ie1bf2760a8f21c38a9466ff945d553e0e293a363 Signed-off-by: Chris Kay chris.kay@arm.com