platform/x86: intel-vbtn: support panel front button

The Lenovo Helix 2 and Dell XPS 12 (9Q33) have an extra button on the
front showing a 'Windows' logo, both reporting event codes 0xC2/0xC3
on press/release. On the Dell, both press/release are distinct events
while on the Helix 2 both events are generated on release.

Tested on XPS 12, for info on the Helix 2 see:
https://www.spinics.net/lists/ibm-acpi-devel/msg03982.html

Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>

drivers/platform/x86/intel-vbtn.c

@@ -38,6 +38,8 @@ static const struct acpi_device_id intel_vbtn_ids[] = {
 static const struct key_entry intel_vbtn_keymap[] = {
 	{ KE_KEY, 0xC0, { KEY_POWER } },	/* power key press */
 	{ KE_IGNORE, 0xC1, { KEY_POWER } },	/* power key release */
+	{ KE_KEY, 0xC2, { KEY_LEFTMETA } },		/* 'Windows' key press */
+	{ KE_KEY, 0xC3, { KEY_LEFTMETA } },		/* 'Windows' key release */
 	{ KE_KEY, 0xC4, { KEY_VOLUMEUP } },		/* volume-up key press */
 	{ KE_IGNORE, 0xC5, { KEY_VOLUMEUP } },		/* volume-up key release */
 	{ KE_KEY, 0xC6, { KEY_VOLUMEDOWN } },		/* volume-down key press */