arm64: Allow masking protection bits in GPA

While converting a gpa to host va, we should take care to mask the "aliased"
IPAs we are dealing with for Realms. The memory slots are defined based on the
plain address without protection attritbutes and as such we should mask the
"alias" bit while translating.

Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>