acpi/acpigen.h: Add more intuitive AML package closing functions

Until now every AML package had to be closed using acpigen_pop_len().
This commit introduces set of package closing functions corresponding
with their opening function names. For example acpigen_write_if()
opens if-statement package, acpigen_write_if_end() closes it.
Now acpigen_write_else() closes previously opened acpigen_write_if(),
so acpigen_pop_len() is not required before it.

Signed-off-by: Jakub Czapiga <jacz@semihalf.com>
Change-Id: Icfdc3804cd93bde049cd11dec98758b3a639eafd
Reviewed-on: https://review.coreboot.org/c/coreboot/+/50910
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Lance Zhao
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/drivers/intel/usb4/retimer/retimer.c

@@ -77,7 +77,6 @@ static void usb4_retimer_cb_set_power_state(void *arg)
 	 */
 	acpigen_write_if_lequal_op_int(LOCAL0_OP, 0);
 	acpigen_disable_tx_gpio(power_gpio);
-	acpigen_pop_len(); /* If */
 
 	/*
 	 * Else {