feat(rmm): add support for the 2nd DRAM bank

feat(rmm): add support for the 2nd DRAM bank

This patch adds support for RMM granules allocation
in FVP 2nd DRAM 2GB bank at 0x880000000 base address.
For ENABLE_RME = 1 case it also removes "mem=1G"
Linux kernel command line option in fvp-base-psci-common.dsti
to allow memory layout discovery from the FVP device tree.
FVP parameter 'bp.dram_size' - size of main memory in gigabytes
documented in docs/components/realm-management-extension.rst
is changed from 2 to 4.

Signed-off-by: AlexeiFedorov <Alexei.Fedorov@arm.com>
Change-Id: I174da4416ad5a8d41bf0ac89f356dba7c0cd3fe7