qcom: smb-lib: make smb_irq_info common for smb2 and smb138x chargers

Since the interrupt information for both smb2 and smb138x charger
devices are almost common, abstract it to a single smb_irq_info
struct. Also, keep an interrupt index for every interrupt which
can be used when necessary.

Change-Id: I4e42dd15a46b59c1a9c27412ca6fdff281fa71ec
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>