ARM: local timers: Interrupt registration mechanism

Register interrupts using interrupt action mechanism instead of
gic_request_ppi() which is dependent on an another patch series
that doesn't exist yet.

Add read_current_timer() to support ARCH_HAS_READ_CURRENT_TIMER
and register the delay loop routine.

Change-Id: I2e7309b93a7bdae37103b738d547eb20f86fe9f7
Signed-off-by: Sathish Ambley <sambley@codeaurora.org>