acpigen_ps2_keybd: map KEY_HOMEPAGE to 0xaa scancode and TK_HOME

Chromium OS EC has some specialized handling of chromebook specific
function keys on the keyboard top row, these have a function specific
action key code that is exposed to the OS and used to map their
position, and also a specific scancode that has to be mapped to a Linux
event code.

This adds the necessary mapping for KEY_HOMEPAGE, which is going to be
used in new devices.

The scancode picked is 0xe012, which maps to e02a or 0xaa, the
corresponding EC CL is:

https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/7118961

BUG=b:446007724
TEST=flashed and tested on a brox board with chromiumos, checked the
code with evtest

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>
Change-Id: I395721a342f507453dae19373df2f189ac1b5dac
Reviewed-on: https://review.coreboot.org/c/coreboot/+/90024
Reviewed-by: Subrata Banik <subratabanik@google.com>
Reviewed-by: Caveh Jalali <caveh@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>

src/include/acpi/acpigen_ps2_keybd.h

@@ -30,6 +30,7 @@ enum ps2_action_key {
 	PS2_KEY_DICTATE,
 	PS2_KEY_ACCESSIBILITY,
 	PS2_KEY_DO_NOT_DISTURB,
+	PS2_KEY_HOMEPAGE,
 };
 
 #define PS2_MIN_TOP_ROW_KEYS		2