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/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.