pvpanic: move pvpanic to misc as common driver

Move pvpanic.c from drivers/platform/x86 to drivers/misc.
Following patches will use pvpanic device in arm64.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Peng Hao <peng.hao2@zte.com.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>