spmi: pmic_arb: don't synchronize accesses to interrupt region

The current driver ensures that no read/write transaction is in progress
while it makes changes to the interrupt regions. This is not necessary
because read/writes over spmi and arbiter interrupt control are
independent operations.

Change-Id: Id6a93eed0aabe55a4b655a2050c31b48327dffe4
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>