platform/x86: thinkpad_acpi: Allow the FnLock LED to change state

platform/x86: thinkpad_acpi: Allow the FnLock LED to change state

On many recent ThinkPad laptops, there's a new LED next to the ESC key,
that indicates the FnLock status.
When the Fn+ESC combo is pressed, FnLock is toggled, which causes the
Media Key functionality to change, making it so that the media keys
either perform their media key function, or function as an F-key by
default. The Fn key can be used the access the alternate function at any
time.

With the current linux kernel, the LED doens't change state if you press
the Fn+ESC key combo. However, the media key functionality *does*
change. This is annoying, since the LED will stay on if it was on during
bootup, and it makes it hard to keep track what the current state of the
FnLock is.

This patch calls an ACPI function, that gets the current media key
state, when the Fn+ESC key combo is pressed. Through testing it was
discovered that this function causes the LED to update correctly to
reflect the current state when this function is called.

The relevant ACPI calls are the following:
\_SB_.PCI0.LPC0.EC0_.HKEY.GMKS: Get media key state, returns 0x603 if the FnLock mode is enabled, and 0x602 if it's disabled.
\_SB_.PCI0.LPC0.EC0_.HKEY.SMKS: Set media key state, sending a 1 will enable FnLock mode, and a 0 will disable it.

Relevant discussion:
https://bugzilla.kernel.org/show_bug.cgi?id=207841
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1881015

Signed-off-by: Esteve Varela Colominas <esteve.varela@gmail.com>
Link: https://lore.kernel.org/r/20210315195823.23212-1-esteve.varela@gmail.com
Signed-off-by: Hans de Goede <hdegoede@redhat.com>