OMAP4/5: Make the silicon revision variable common.

The different silicon revision variable names was defined for OMAP4 and
OMAP5 socs. Making the variable common so that some code can be
made generic.

Signed-off-by: R Sricharan <r.sricharan@ti.com>

arch/arm/include/asm/omap_common.h

@@ -108,6 +108,12 @@ void spl_ymodem_load_image(void);
 void spl_board_init(void);
 #endif
 
+static inline u32 omap_revision(void)
+{
+	extern u32 *const omap_si_rev;
+	return *omap_si_rev;
+}
+
 /*
  * silicon revisions.
  * Moving this to common, so that most of code can be moved to common,