Platform: Add an option to run code in SPE from RAM

Define new TFM_RAM_CODE SRAM region in gcc and clang linker
scripts for code with .ramfunc attribute. This region is
intended for privileged secure code running from SRAM.

Signed-off-by: Andrei Narkevitch <ainh@cypress.com>
Change-Id: I4ab72f878271f20d28dbdd1cbfb84ed814c16caf