ARM: 8931/1: Add clock_getres entry point

The generic vDSO library provides an implementation of clock_getres() that
can be leveraged by each architecture.

Add clock_getres() entry point on arm to be on pair with arm64.

Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>