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/include/imx8m_psci.h b/plat/imx/imx8m/include/imx8m_psci.h
index c33d25e..7d14d11 100644
--- a/plat/imx/imx8m/include/imx8m_psci.h
+++ b/plat/imx/imx8m/include/imx8m_psci.h
@@ -19,5 +19,6 @@
 void imx_domain_suspend(const psci_power_state_t *target_state);
 void imx_domain_suspend_finish(const psci_power_state_t *target_state);
 void __dead2 imx_pwr_domain_pwr_down_wfi(const psci_power_state_t *target_state);
+int imx_system_reset2(int is_vendor, int reset_type, u_register_t cookie);
 
 #endif /* IMX8M_PSCI_H */