arm64: Use Normal NonCacheable memory for writecombine

This provides better performance compared to Device GRE and also allows
unaligned accesses. Such memory is intended to be used with standard RAM
(e.g. framebuffers) and not I/O.
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/pgtable.h

@@ -254,7 +254,7 @@ static inline int has_transparent_hugepage(void)
 #define pgprot_noncached(prot) \
 	__pgprot_modify(prot, PTE_ATTRINDX_MASK, PTE_ATTRINDX(MT_DEVICE_nGnRnE))
 #define pgprot_writecombine(prot) \
-	__pgprot_modify(prot, PTE_ATTRINDX_MASK, PTE_ATTRINDX(MT_DEVICE_GRE))
+	__pgprot_modify(prot, PTE_ATTRINDX_MASK, PTE_ATTRINDX(MT_NORMAL_NC))
 #define pgprot_dmacoherent(prot) \
 	__pgprot_modify(prot, PTE_ATTRINDX_MASK, PTE_ATTRINDX(MT_NORMAL_NC))
 #define __HAVE_PHYS_MEM_ACCESS_PROT