armv8: add cpu core helper functions

Add helper functions to identify different armv8 variants.
Signed-off-by: NPeng Fan <peng.fan@nxp.com>
Reviewed-by: NAnatolij Gustschin <agust@denx.de>
Cc: Stefano Babic <sbabic@denx.de>

arch/arm/include/asm/armv8/cpu.h

+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright 2018 NXP
+ */
+
+#define MIDR_PARTNUM_CORTEX_A35	0xD04
+#define MIDR_PARTNUM_CORTEX_A53	0xD03
+#define MIDR_PARTNUM_CORTEX_A72	0xD08
+#define MIDR_PARTNUM_SHIFT	0x4
+#define MIDR_PARTNUM_MASK	(0xFFF << 0x4)
+
+static inline unsigned int read_midr(void)
+{
+	unsigned long val;
+
+	asm volatile("mrs %0, midr_el1" : "=r" (val));
+
+	return val;
+}
+
+#define is_cortex_a35() (((read_midr() & MIDR_PARTNUM_MASK) >> \
+			 MIDR_PARTNUM_SHIFT) == MIDR_PARTNUM_CORTEX_A35)
+#define is_cortex_a53() (((read_midr() & MIDR_PARTNUM_MASK) >> \
+			 MIDR_PARTNUM_SHIFT) == MIDR_PARTNUM_CORTEX_A53)
+#define is_cortex_a72() (((read_midr() & MIDR_PARTNUM_MASK) >>\
+			 MIDR_PARTNUM_SHIFT) == MIDR_PARTNUM_CORTEX_A72)