bus: mhi: core: Add support for reading MHI info from device

The MHI register base has several registers used for getting the MHI
specific information such as version, family, major, and minor numbers
from the device. This information can be used by the controller drivers
for usecases such as applying quirks for a specific revision etc...

While at it, let's also rearrange the local variables
in mhi_register_controller().

Suggested-by: Hemant Kumar <hemantk@codeaurora.org>
Reviewed-by: Jeffrey Hugo <jhugo@codeaurora.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20200324061050.14845-3-manivannan.sadhasivam@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>