arm64: module: create module allocations without exec permissions

Now that the core code manages the executable permissions of code
regions of modules explicitly, it is no longer necessary to create
the module vmalloc regions with RWX permissions, and we can create
them with RW- permissions instead, which is preferred from a
security perspective.

Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>