spmi-pmic-arb: Add support for varying number of channels

Add the max pmic arb supported channel, interrupts as part
of spmi controller to support varying max channel and
interrupts from target to target with same arbiter version.

Change-Id: I96f146f0c0d2d9a4442a38ca94f131e52f862205
Signed-off-by: Alok Chauhan <alokc@codeaurora.org>