arm64: mte: Validate the PROT_MTE request via arch_validate_flags()

Make use of the newly introduced arch_validate_flags() hook to
sanity-check the PROT_MTE request passed to mmap() and mprotect(). If
the mapping does not support MTE, these syscalls will return -EINVAL.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>