ANDROID: firmware/psci: Remove PSCI_1_1_FN64_MEM_PROTECT definition

The PSCI MEM_PROTECT function does not have a 64-bit function identifier,
so remove the unused definition which was erroneously left intact when
applying fe3157f3 ("ANDROID: KVM: arm64: Use 32-bit function ID for
PSCI MEM_PROTECT call").

Bug: 260316363
Cc: Quentin Perret <qperret@google.com>
Signed-off-by: Will Deacon <willdeacon@google.com>
Change-Id: Ica948b202bf01175b6ab0961307899d269649880