mips: refactor disabling of caches

Logically this code belongs to cache_init.S.

If a complex SoC needs to replace the generic cache init,
mips_cache_disable() can now be called from custom start.S files.

Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Tested-by: Stefan Roese <sr@denx.de>
diff --git a/arch/mips/cpu/start.S b/arch/mips/cpu/start.S
index c3d1e64..a9f8743 100644
--- a/arch/mips/cpu/start.S
+++ b/arch/mips/cpu/start.S
@@ -196,11 +196,10 @@
 	mtc0	zero, CP0_COMPARE
 
 #ifndef CONFIG_SKIP_LOWLEVEL_INIT
-	mfc0	t0, CP0_CONFIG
-	and	t0, t0, MIPS_CONF_IMPL
-	or	t0, t0, CONF_CM_UNCACHED
-	mtc0	t0, CP0_CONFIG
-	ehb
+	/* Disable caches */
+	PTR_LA	t9, mips_cache_disable
+	jalr	t9
+	 nop
 #endif
 
 #ifdef CONFIG_MIPS_CM
diff --git a/arch/mips/lib/cache_init.S b/arch/mips/lib/cache_init.S
index 2233d27..602741c 100644
--- a/arch/mips/lib/cache_init.S
+++ b/arch/mips/lib/cache_init.S
@@ -418,6 +418,12 @@
 	jr	R_RETURN
 	END(mips_cache_reset)
 
+LEAF(mips_cache_disable)
+	move	R_RETURN, ra
+	change_k0_cca_kseg1 CONF_CM_UNCACHED
+	jr	R_RETURN
+	END(mips_cache_disable)
+
 LEAF(change_k0_cca)
 	mfc0		t0, CP0_CONFIG
 #if __mips_isa_rev >= 2