drivers: qcom: sdx_ext_ipc: notify remote processor wokeup

When the remote processor wants to wake up local processor
it toggles one of the GPIO. The IRQ handler at local
end will notify registered listeners about it.

Change-Id: Iccbfb7c86538c1e111c97bbe438ef5846182405e
Signed-off-by: Rishi Gupta <rishgupt@codeaurora.org>
Signed-off-by: Yogesh Lal <ylal@codeaurora.org>