arm64: compat: Hook up io_pgetevents() for 32-bit tasks

Commit 73aeb2cb

 ("ARM: 8787/1: wire up io_pgetevents syscall")
hooked up the io_pgetevents() system call for 32-bit ARM, so we can
do the same for the compat wrapper on arm64.

Signed-off-by: Will Deacon <will.deacon@arm.com>