ARM: Add workaround for Cortex-A9 errata 794072

A short loop including a DMB instruction might cause a denial of
service on another processor which executes a CP15 broadcast operation.
Exists on r1, r2, r3, r4 revisions.

Signed-off-by: Nitin Garg <nitin.garg@freescale.com>
Acked-by: Dirk Behme <dirk.behme@de.bosch.com>

README

@@ -566,6 +566,7 @@ The following options need to be configured:
 		CONFIG_ARM_ERRATA_742230
 		CONFIG_ARM_ERRATA_743622
 		CONFIG_ARM_ERRATA_751472
+		CONFIG_ARM_ERRATA_794072
 
 		If set, the workarounds for these ARM errata are applied early
 		during U-Boot startup. Note that these options force the

arch/arm/cpu/armv7/start.S

@@ -205,7 +205,7 @@ ENTRY(cpu_init_cp15)
 	mcr	p15, 0, r0, c1, c0, 0	@ write system control register
 #endif
 
-#ifdef CONFIG_ARM_ERRATA_742230
+#if (defined(CONFIG_ARM_ERRATA_742230) || defined(CONFIG_ARM_ERRATA_794072))
 	mrc	p15, 0, r0, c15, c0, 1	@ read diagnostic register
 	orr	r0, r0, #1 << 4		@ set bit #4
 	mcr	p15, 0, r0, c15, c0, 1	@ write diagnostic register