In preparation of the endpoint MHI support, let's move the host MHI code
to its own "host" directory and adjust the toplevel MHI Kconfig & Makefile.

While at it, let's also move the "pci_generic" driver to "host" directory
as it is a host MHI controller driver.
Reviewed-by: NHemant Kumar <hemantk@codeaurora.org>
Reviewed-by: NAlex Elder <elder@linaro.org>
Signed-off-by: NManivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20220301160308.107452-5-manivannan.sadhasivam@linaro.orgSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>