drivers: qcom: rpmh: rename rpmh_write_passthru to rpmh_write_batch

rpmh_write_passthru() was meant to be a call which did not cache the
RPMH requests in the driver. However, with some new optimizations, we
now cache even the requests sent as a batch through the passthru api.
Hence rename the api to rpmh_write_batch() to reflect the functionality.

Change-Id: Ib97f4cc80db415f4313fbb111faf23b002d4ca97
Signed-off-by: Lina Iyer <ilina@codeaurora.org>