acpigen_ps2_keybd: Add assistant key to linux,keymap

If the ChromiumOS EC indicates that the device has an assistant key,
we should also add it to the generated linux,keymap binding.  This
commit simply does so by examining the keyboard capabilities reported by
the EC.

BUG=b:333088656
TEST=With a device that has an assistant key, flash AP FW and verify
that the key is mapped to `KEY_ASSISTANT` in the Linux kernel using
`evtest`.

Change-Id: I217220e89bce88e3045a4fc3b124954696276442
Signed-off-by: Aseda Aboagye <aaboagye@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/81996
Reviewed-by: Jonathon Hall <jonathon.hall@puri.sm>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Caveh Jalali <caveh@chromium.org>

src/include/acpi/acpigen_ps2_keybd.h

@@ -37,6 +37,7 @@ void acpigen_ps2_keyboard_dsd(const char *scope, uint8_t num_top_row_keys,
 			      enum ps2_action_key action_keys[],
 			      bool can_send_function_keys,
 			      bool has_numeric_keypad, bool has_scrnlock_key,
+			      bool has_assistant_key,
 			      bool has_alpha_num_punct_keys);
 
 #endif /* __ACPI_ACPIGEN_PS2_KEYBD_H__ */