Build: Create a common lib and copy it to the RAM for flash drivers

For some boards is it necessary to run the flash drivers from the RAM
(FW upgrade, XIP/QSPI flash mode). This common lib can be used for
this purpose, when S_CODE_SRAM_ALIAS_BASE and TOTAL_CODE_SRAM_SIZE
are set. This patch also removes Musca-B1 related object files from
common linker scripts.

Signed-off-by: Dávid Házi <david.hazi@arm.com>
Change-Id: I44293c66c3cd29eb8897c2e484f0dc3e5781507c