bus: mhi: pci_generic: Introduce Sierra EM919X support

bus: mhi: pci_generic: Introduce Sierra EM919X support

Add support for EM919X modems, this modem series is based on SDX55
qcom chip.

It is mandatory to use the same ring for control+data and diag events.

Signed-off-by: Thomas Perrot <thomas.perrot@bootlin.com>
Tested-by: Aleksander Morgado <aleksander@aleksander.es>
Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>
Link: https://lore.kernel.org/r/20211123081541.648426-1-thomas.perrot@bootlin.com
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>