aemfvp-a-rme: overlay distro and uefi firmware on FVP host os

For Q1'24 aemfvp-a-rme release adding the support for overlaying the needed
debian distro image and kvmtool firmware for doing uefi boot of distro in
realm security state. Changes include
- increasing the size of buildroot FS to contain distro images.
- copying distro image and firmware in case UEFI_RME_BUILD_ENABLED is enabled
  and there is a distro image in rme/distro-images path.
- CTX_INCLUDE_MTE_REGS option is deprecated, using ENABLE_FEAT_MTE

Signed-off-by: nitin sharma <nitin.sharma3@arm.com>
Change-Id: Ide4f515450c91beb3368903020677f88ac910bde