msm: pil: Move device tree parsing code into the framework

Every driver has to repeat the code for parsing device tree nodes for the
proxy unvote IRQ. So, move this parsing code into the framework level to
avoid this duplication of code.

Change-Id: I8739af63f6f3bc95aaded74d60359256e5bd7a66
Signed-off-by: Seemanta Dutta <seemanta@codeaurora.org>