ARM: imx: remove stale mx53_display_revision() declaration

The mx53_display_revision() declaration in common.h is stale and used
nowhere, so remove it.
Signed-off-by: NShawn Guo <shawn.guo@linaro.org>

arch/arm/mach-imx/common.h

@@ -73,7 +73,6 @@ extern void mxc_restart(enum reboot_mode, const char *);
 extern void mxc_arch_reset_init(void __iomem *);
 extern void mxc_arch_reset_init_dt(void);
 extern int mx53_revision(void);
-extern int mx53_display_revision(void);
 extern void imx_set_aips(void __iomem *);
 extern int mxc_device_init(void);
 void imx_set_soc_revision(unsigned int rev);