regmap: call regmap_raw_multi_reg_write from regcache sync

Call regmap_raw_multi_reg_write API from regcache sync to sync
multiple registers to the hardware if bus interface supports
multi register write. This change will help in reducing the
latency for syncing the registers to the hardware.

Change-Id: I94d19434dc7465434f10db9f7bd62fcc8246d845
Signed-off-by: Sudheer Papothi <spapothi@codeaurora.org>