proc: test ProtectionKey in proc-empty-vm test

Check ProtectionKey field in /proc/*/smaps output, if system supports
protection keys feature.

[adobriyan@gmail.com: test support in the beginning of the program, use syscall, not glibc pkey_alloc(3) which may not compile]

Link: https://lkml.kernel.org/r/ac05efa7-d2a0-48ad-b704-ffdd5450582e@p183


Signed-off-by: Swarup Laxman Kotiaklapudi <swarupkotikalapudi@gmail.com>
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Reviewed-by: Swarup Laxman <Kotikalapudi&lt;swarupkotikalapudi@gmail.com>
Tested-by: Swarup Laxman <Kotikalapudi&lt;swarupkotikalapudi@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>