drivers: mfd: Add support for multi register writes of each page

wcd9335 has multiple pages with each page has set of registers.
slimbus supports writing multiple registers in one transaction.
Change enables writing set of registers of each page of wcd9335
codec in one slimbus transaction. This will help reduce the
latency during codec register writes.

Change-Id: I4282ca9787d23c097f6ec031d4986898376c6b25
Signed-off-by: Sudheer Papothi <spapothi@codeaurora.org>