spd: tlkd: secure timer interrupt handler

This patch adds an interrupt handler for TLK. On receiving an
interrupt, the source of the interrupt is determined and the
interrupt is marked complete. The IRQ number is passed to
TLK along with a special SMC function ID. TLK issues an SMC
to notify completion of the interrupt handler in the S-EL1
world.

Change-Id: I76f28cee6537245c5e448d2078f86312219cea1a
Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>