Move display_end before secmon + add boolean supp.

Currently bpmp loses access to the relevant registers when secmon or exosphere is launched.

This change provides support for all firmwares and properly sanitizes the display.

common/common_gfx.h

@@ -40,5 +40,5 @@ typedef struct _gfx_con_t
 	u32 fgcol;
 	int fillbg;
 	u32 bgcol;
-	int mute;
+	bool mute;
 } gfx_con_t;