MIPS: zboot: head.S clean up

.cprestore is removed as we don't expect Position Independent
zboot ELF.

.noreorder is also removed and rest instructions are massaged
to improve readability.

t9 register is used for indirect jump as MIPS ABI requirement.

start label is removed as it already defined in LEAF.
Reported-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Reviewed-by: Huacai Chen <chenhuacai@kernel.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/boot/compressed/head.S

@@ -15,10 +15,7 @@
 #include <asm/asm.h>
 #include <asm/regdef.h>
 
-	.set noreorder
-	.cprestore
 	LEAF(start)
-start:
 	/* Save boot rom start args */
 	move	s0, a0
 	move	s1, a1
@@ -35,21 +32,20 @@ start:
 	PTR_LA	a0, (.heap)	     /* heap address */
 	PTR_LA	sp, (.stack + 8192)  /* stack address */
 
-	PTR_LA	ra, 2f
-	PTR_LA	k0, decompress_kernel
-	jr	k0
-	 nop
+	PTR_LA	t9, decompress_kernel
+	jalr	t9
+
 2:
 	move	a0, s0
 	move	a1, s1
 	move	a2, s2
 	move	a3, s3
-	PTR_LI	k0, KERNEL_ENTRY
-	jr	k0
-	 nop
+	PTR_LI	t9, KERNEL_ENTRY
+	jalr	t9
+
 3:
 	b	3b
-	 nop
+
 	END(start)
 
 	.comm .heap,BOOT_HEAP_SIZE,4