ANDROID: arch: add missing pidfd_open definitions for arm32

While backporting commit 7615d9e1780e26e0178c93c55b73309a5dc093d7 to 4.9
arm32 definitions for pidfd_open syscall were not added correctly. Fix
by adding missing definitions.

Fixes aosp/986706 "BACKPORT: arch: wire-up pidfd_open()"

Bug: 135608568
Test: make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf-
Change-Id: I68b8454971f296453d598de281ebe9225067f0b8
Signed-off-by: Suren Baghdasaryan <surenb@google.com>