MIPS: make inclusion of ROM exception vectors configurable

This adds a compile time option to include code for static
exception vectors. Static exception vectors are only needed,
when the U-Boot entry point is equal to the CPU reset exception
vector address. For instance this is the case when U-Boot is
used as ROM in Qemu or booted from parallel NOR flash. When
U-Boot is booted from RAM (e.g. loaded there by SPL), the
exception vectors need to be setup dynamically, which is done
in follow-up commits.

Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
diff --git a/arch/mips/cpu/start.S b/arch/mips/cpu/start.S
index 3f0fc12..108d2df 100644
--- a/arch/mips/cpu/start.S
+++ b/arch/mips/cpu/start.S
@@ -57,7 +57,6 @@
 	b	reset
 	 nop
 
-	.org 0x10
 #if defined(CONFIG_SYS_XWAY_EBU_BOOTCFG)
 	/*
 	 * Almost all Lantiq XWAY SoC devices have an external bus unit (EBU) to
@@ -66,16 +65,20 @@
 	 * initial configuration for that EBU in order to access the flash
 	 * device with correct parameters. This config option is board-specific.
 	 */
+	.org 0x10
 	.word CONFIG_SYS_XWAY_EBU_BOOTCFG
 	.word 0x0
-#elif defined(CONFIG_MALTA)
+#endif
+#if defined(CONFIG_MALTA)
 	/*
 	 * Linux expects the Board ID here.
 	 */
+	.org 0x10
 	.word 0x00000420	# 0x420 (Malta Board with CoreLV)
 	.word 0x00000000
 #endif
 
+#if defined(CONFIG_ROM_EXCEPTION_VECTORS)
 	.org 0x200
 	/* TLB refill, 32 bit task */
 1:	b	1b
@@ -106,7 +109,9 @@
 1:	b	1b
 	 nop
 
-	.align 4
+	.org 0x500
+#endif
+
 reset:
 #if __mips_isa_rev >= 6
 	mfc0	t0, CP0_CONFIG, 5