par_master: Add shutdown function in par_master struct

With this, register_par_master can take care of register_shutdown
as well, and every par master only needs to call
register_par_master instead of calling both register_par_master
and register_shutdown.

Next patches in the chain convert par masters to use new API.

Tested: builds and ninja test

Change-Id: I0fee15d548cdd16678e551eeb351e659812ddf76
Signed-off-by: Anastasia Klimchuk <aklm@chromium.org>
Original-Reviewed-on: https://review.coreboot.org/c/flashrom/+/57154
Original-Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>
Reviewed-on: https://review.coreboot.org/c/flashrom-stable/+/72232
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/programmer.h b/programmer.h
index deaafc4..d392027 100644
--- a/programmer.h
+++ b/programmer.h
@@ -425,6 +425,7 @@
 	uint16_t (*chip_readw) (const struct flashctx *flash, const chipaddr addr);
 	uint32_t (*chip_readl) (const struct flashctx *flash, const chipaddr addr);
 	void (*chip_readn) (const struct flashctx *flash, uint8_t *buf, const chipaddr addr, size_t len);
+	int (*shutdown)(void *data);
 	void *data;
 };
 int register_par_master(const struct par_master *mst, const enum chipbustype buses, void *data);