sysreset: move stm32mp sysreset poweroff implementation to sysreset uclass

This is a generic implementation. Add CONFIG_SYSRESET_CMD_POWEROFF
to signal when we need it. Enable it from the STPMIC1 config and in
sandbox.

The config flag is transitionary, that is it can be removed after all
poweroff implementations use sysreset, and just have CMD_POWEROFF depend
on sysreset.

Signed-off-by: Urja Rannikko <urjaman@gmail.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@st.com>
Tested-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/drivers/sysreset/Kconfig b/drivers/sysreset/Kconfig
index 90c41ab..f565ae0 100644
--- a/drivers/sysreset/Kconfig
+++ b/drivers/sysreset/Kconfig
@@ -33,6 +33,16 @@
 
 if SYSRESET
 
+if CMD_POWEROFF
+
+config SYSRESET_CMD_POWEROFF
+	bool "sysreset implementation of the poweroff command"
+	help
+	  This should be selected by the appropriate PMIC driver if
+	  the poweroff command is enabled.
+
+endif
+
 config SYSRESET_GPIO
 	bool "Enable support for GPIO reset driver"
 	select DM_GPIO