arm: imx: hab: Define rvt_failsafe()

The hab_rvt_failsafe() callback according to the HABv4 documentation:

"This function provides a safe path when image authentication has failed
and all possible boot paths have been exhausted. It is intended for use by
post-ROM boot stage components, via the ROM Vector Table."

Once invoked the part will drop down to its BootROM USB recovery mode.
Should it be the case that the part is in secure boot mode - only an
appropriately signed binary will be accepted by the ROM and subsequently
executed.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Albert Aribaud <albert.u.boot@aribaud.net>
Cc: Sven Ebenfeld <sven.ebenfeld@gmail.com>
Cc: George McCollister <george.mccollister@gmail.com>
Cc: Breno Matheus Lima <brenomatheus@gmail.com>
Tested-by: Breno Lima <breno.lima@nxp.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>

arch/arm/include/asm/mach-imx/hab.h

@@ -140,6 +140,7 @@ typedef void *hab_rvt_authenticate_image_t(uint8_t, ptrdiff_t,
 		void **, size_t *, hab_loader_callback_f_t);
 typedef enum hab_status hab_rvt_check_target_t(enum hab_target, const void *,
 					       size_t);
+typedef void hab_rvt_failsafe_t(void);
 typedef void hapi_clock_init_t(void);
 
 #define HAB_ENG_ANY		0x00   /* Select first compatible engine */
@@ -170,6 +171,7 @@ typedef void hapi_clock_init_t(void);
 #define HAB_RVT_AUTHENTICATE_IMAGE	(*(uint32_t *)(HAB_RVT_BASE + 0x10))
 #define HAB_RVT_REPORT_EVENT		(*(uint32_t *)(HAB_RVT_BASE + 0x20))
 #define HAB_RVT_REPORT_STATUS		(*(uint32_t *)(HAB_RVT_BASE + 0x24))
+#define HAB_RVT_FAILSAFE		(*(uint32_t *)(HAB_RVT_BASE + 0x28))
 
 #define HAB_RVT_REPORT_EVENT_NEW               (*(uint32_t *)0x000000B8)
 #define HAB_RVT_REPORT_STATUS_NEW              (*(uint32_t *)0x000000BC)