msm: msm_bus: export msm_bus_fabric_init_driver

I2c-qup driver is a client of msm_bus_fabric driver while drivers like
onsemi-ncp6335d and fan53555 are clients of i2c-qup driver. In some
targets, onsemi-ncp6335d and fan53555 drivers have to initialize and probe
early before the i2c-qup and msm_bus_fabric driver are ready. Hence export
msm_bus_fabric_init_driver to make sure msm_bus_fabric driver is ready when
its clients need to probe.

Change-Id: Ifa4f43d04f5261c49279ed9ff0e232e215066070
Signed-off-by: Ke Liu <keliu@codeaurora.org>