riscv: Introduce CONFIG_XIP to support booting from flash

When U-Boot boots from flash, during the boot process,
hart_lottery and available_harts_lock variable addresses
point to flash which is not writable. This causes boot
failures on AE350. Introduce a config option CONFIG_XIP
to support such configuration.

Signed-off-by: Rick Chen <rick@andestech.com>
Cc: Greentime Hu <greentime@andestech.com>
Reviewed-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/riscv/cpu/start.S b/arch/riscv/cpu/start.S
index a4433fb..3402d09 100644
--- a/arch/riscv/cpu/start.S
+++ b/arch/riscv/cpu/start.S
@@ -98,6 +98,7 @@
 	mv	sp, a0
 #endif
 
+#ifndef CONFIG_XIP
 	/*
 	 * Pick hart to initialize global data and run U-Boot. The other harts
 	 * wait for initialization to complete.
@@ -106,6 +107,9 @@
 	li	s2, 1
 	amoswap.w s2, t1, 0(t0)
 	bnez	s2, wait_for_gd_init
+#else
+	bnez	tp, secondary_hart_loop
+#endif
 
 	la	t0, prior_stage_fdt_address
 	SREG	s1, 0(t0)
@@ -115,6 +119,7 @@
 	/* save the boot hart id to global_data */
 	SREG	tp, GD_BOOT_HART(gp)
 
+#ifndef CONFIG_XIP
 	la	t0, available_harts_lock
 	fence	rw, w
 	amoswap.w zero, zero, 0(t0)
@@ -141,6 +146,7 @@
 	 * secondary_hart_loop.
 	 */
 	bnez	s2, secondary_hart_loop
+#endif
 
 	/* Enable cache */
 	jal	icache_enable