platform/chrome: cros_ec_lpc: Only check for events on MKBP notifies

platform/chrome: cros_ec_lpc: Only check for events on MKBP notifies

Only check EC for MKBP events when the ACPI notify value indicates the
notify is due to an MKBP host event. This reduces unnecessary queries to
the EC.

Notify value 0x80 is reserved for devices specific notifies. It is used
by many devices to indicate various events. It's only used by cros_ec
for MKBP events.

Signed-off-by: Rob Barnes <robbarnes@google.com>
Link: https://lore.kernel.org/r/20241218015759.3558830-1-robbarnes@google.com
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>