qemu/qemu_sbsa: Adding Qemu SBSA platform ...

This patch introduces Qemu SBSA platform.
Both platform specific files where copied from qemu/qemu with changes for
DRAM base above 32bit and removal of ARMv7 conditional defines/code.
Documentation is aligned to rest of SBSA patches along the series and
planed changes in edk2-platform repo.

Fixes ARM-software/tf-issues#602

Signed-off-by: Radoslaw Biernacki <radoslaw.biernacki@linaro.org>
Change-Id: I8ebc34eedb2268365e479ef05654b2df1b99128c