acpigen_ps2_keybd: Support an Accessibility key

Add support for an Accessibility key. HUTRR116 added support for a new
usage titled "System Accessibility Binding" which toggles a
system-wide bound accessibility UI or command.

BUG=b:333095388
TEST=Build and flash a board that contains an accessibility key. Verify
that KEY_ACCESSIBILITY is generated in the Linux kernel with patches[0]
that add this new event code using `evtest`.
```
Testing ... (interrupt to exit)
Event: time 1718924048.882841, -------------- SYN_REPORT ------------
Event: time 1718924054.062428, type 4 (EV_MSC), code 4 (MSC_SCAN), value a9
Event: time 1718924054.062428, type 1 (EV_KEY), code 590 (?), value 1
Event: time 1718924054.062428, -------------- SYN_REPORT ------------
Event: time 1718924054.195904, type 4 (EV_MSC), code 4 (MSC_SCAN), value a9
Event: time 1718924054.195904, type 1 (EV_KEY), code 590 (?), value 0
Event: time 1718924054.195904, -------------- SYN_REPORT ------------
```

[0] - https://git.kernel.org/pub/scm/linux/kernel/git/hid/hid.git/commit/?id=0c7dd00de018ff70b3452c424901816e26366a8a

Change-Id: Ifc639b37e89ec251f55859331ab5c2f4b2b45a7d
Signed-off-by: Aseda Aboagye <aaboagye@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/82996
Reviewed-by: Caveh Jalali <caveh@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Forest Mittelberg <bmbm@google.com>
diff --git a/src/include/acpi/acpigen_ps2_keybd.h b/src/include/acpi/acpigen_ps2_keybd.h
index 5a55356..fe1101b 100644
--- a/src/include/acpi/acpigen_ps2_keybd.h
+++ b/src/include/acpi/acpigen_ps2_keybd.h
@@ -28,6 +28,7 @@
 	PS2_KEY_MICMUTE,
 	PS2_KEY_MENU,
 	PS2_KEY_DICTATE,
+	PS2_KEY_ACCESSIBILITY,
 };
 
 #define PS2_MIN_TOP_ROW_KEYS		2