bus: mhi: Move host MHI code to "host" directory

[ Upstream commit a0f5a630

 ]

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: Hemant Kumar <hemantk@codeaurora.org>
Reviewed-by: Alex Elder <elder@linaro.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20220301160308.107452-5-manivannan.sadhasivam@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Stable-dep-of: 6a0c637b

 ("bus: mhi: host: Range check CHDBOFF and ERDBOFF")
Signed-off-by: Sasha Levin <sashal@kernel.org>