drm: Add arch arm64 for drm_clflush_virt_range

Use flush_tlb_kernel_range when invoking drm_clflush_virt_range on
arm64 platforms. Using flush_tlb_kernel_range will:

1. Make sure prior page-table updates have been completed
2. Invalidate the TLB
3. Check if the TLB invalidation has been completed

Signed-off-by: Michael Cheng <michael.cheng@intel.com>

drivers/gpu/drm/drm_cache.c

@@ -176,6 +176,10 @@ drm_clflush_virt_range(void *addr, unsigned long length)
 
 	if (wbinvd_on_all_cpus())
 		pr_err("Timed out waiting for cache flush\n");
+
+#elif defined(CONFIG_ARM64)
+	void *end = addr + length;
+	flush_tlb_kernel_range(*addr, *end);
 #else
 	pr_err("Architecture has no drm_cache.c support\n");
 	WARN_ON_ONCE(1);