feat(plat/imx8m): add system_reset2 implementation

Add imx_system_reset2 which extends existing SYSTEM_RESET. It provides
architectural reset definitions and vendor-specific resets.
By default warm reset is triggered.

Also refactor existing implementation of wdog reset, add details about
each flag used.

Change-Id: Ia7348c32c385f1c61f8085776e81dd1e38ddda5c
Signed-off-by: Igor Opaniuk <igor.opaniuk@foundries.io>
diff --git a/plat/imx/imx8m/imx8mm/imx8mm_psci.c b/plat/imx/imx8m/imx8mm/imx8mm_psci.c
index e558724..815d3a2 100644
--- a/plat/imx/imx8m/imx8mm/imx8mm_psci.c
+++ b/plat/imx/imx8m/imx8mm/imx8mm_psci.c
@@ -28,6 +28,7 @@
 	.pwr_domain_pwr_down_wfi = imx_pwr_domain_pwr_down_wfi,
 	.get_sys_suspend_power_state = imx_get_sys_suspend_power_state,
 	.system_reset = imx_system_reset,
+	.system_reset2 = imx_system_reset2,
 	.system_off = imx_system_off,
 };