MAINTAINERS: Update the entry for MHI bus

Since Hemant is not carrying out any maintainership duties let's make
him as a dedicated reviewer. Also add the new mailing lists dedicated
for MHI in subspace mailing list server.

Reviewed-by: Hemant Kumar <hemantk@codeaurora.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20211019133901.173966-1-manivannan.sadhasivam@linaro.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>