Add core support for ARMv6/v7 big-endian

Starting with ARMv6, the CPUs support the BE-8 variant of big-endian
(byte-invariant). This patch adds the core support:

- setting of the BE-8 mode via the CPSR.E register for both kernel and
  user threads
- big-endian page table walking
- REV used to rotate instructions read from memory during fault
  processing as they are still little-endian format
- Kconfig and Makefile support for BE-8. The --be8 option must be passed
  to the final linking stage to convert the instructions to
  little-endian

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm/mm/Kconfig

@@ -639,6 +639,20 @@ config CPU_BIG_ENDIAN
 	  port must properly enable any big-endian related features
 	  of your chipset/board/processor.
 
+config CPU_ENDIAN_BE8
+	bool
+	depends on CPU_BIG_ENDIAN
+	default CPU_V6 || CPU_V7
+	help
+	  Support for the BE-8 (big-endian) mode on ARMv6 and ARMv7 processors.
+
+config CPU_ENDIAN_BE32
+	bool
+	depends on CPU_BIG_ENDIAN
+	default !CPU_ENDIAN_BE8
+	help
+	  Support for the BE-32 (big-endian) mode on pre-ARMv6 processors.
+
 config CPU_HIGH_VECTOR
 	depends on !MMU && CPU_CP15 && !CPU_ARM740T
 	bool "Select the High exception vector"

arch/arm/mm/abort-ev6.S

@@ -37,6 +37,9 @@ ENTRY(v6_early_abort)
 	movne	pc, lr
 	do_thumb_abort
 	ldreq	r3, [r2]			@ read aborted ARM instruction
+#ifdef CONFIG_CPU_ENDIAN_BE8
+	reveq	r3, r3
+#endif
 	do_ldrd_abort
 	tst	r3, #1 << 20			@ L = 0 -> write
 	orreq	r1, r1, #1 << 11		@ yes.

arch/arm/mm/proc-v6.S

@@ -170,6 +170,9 @@ __v6_setup:
 #endif /* CONFIG_MMU */
 	adr	r5, v6_crval
 	ldmia	r5, {r5, r6}
+#ifdef CONFIG_CPU_ENDIAN_BE8
+	orr	r6, r6, #1 << 25		@ big-endian page tables
+#endif
 	mrc	p15, 0, r0, c1, c0, 0		@ read control register
 	bic	r0, r0, r5			@ clear bits them
 	orr	r0, r0, r6			@ set them

arch/arm/mm/proc-v7.S

@@ -253,6 +253,9 @@ __v7_setup:
 	mcr	p15, 0, r6, c10, c2, 1		@ write NMRR
 	adr	r5, v7_crval
 	ldmia	r5, {r5, r6}
+#ifdef CONFIG_CPU_ENDIAN_BE8
+	orr	r6, r6, #1 << 25		@ big-endian page tables
+#endif
    	mrc	p15, 0, r0, c1, c0, 0		@ read control register
 	bic	r0, r0, r5			@ clear bits them
 	orr	r0, r0, r6			@ set them