Move from WMI driver to platform driver. This move is necessary since
the driver is no longer a hotkeys driver only. Platform driver makes it
easier for users to access sysfs attributes under (i.e.
/sys/devices/platform/huawei-wmi) compared to wmi driver.

Use WMI device UID, AMW0 has a UID of HWMI. WMI0 is the device name
and doesn't have a UID so keep it as it is.
Signed-off-by: Ayman Bagabas <ayman.bagabas@gmail.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>