irqchip: Declare the msm_show_resume_irq_mask in a header

msm_show_resume_irq_mask is currently being declared by individual
drivers as needed. However, it creates scalability issues and looks
ugly. Hence, place the variable in a common header file so that the
drivers can just include it.

Change-Id: I35348a6a280c15a5ad4744097f1075f165af1bc8
Signed-off-by: Raghavendra Rao Ananta <rananta@codeaurora.org>