all: fix assembly vet issues

Add missing function prototypes.
Fix function prototypes.
Use FP references instead of SP references.
Fix variable names.
Update comments.
Clean up whitespace. (Not for vet.)

All fairly minor fixes to make vet happy.

Updates #11041

Change-Id: Ifab2cdf235ff61cdc226ab1d84b8467b5ac9446c
Reviewed-on: https://go-review.googlesource.com/27713
Run-TryBot: Josh Bleecher Snyder <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Brad Fitzpatrick <[email protected]>

Author: josharian

src/crypto/rc4/rc4_arm.s

@@ -25,8 +25,8 @@ TEXT ·xorKeyStream(SB),NOSPLIT,$0
 	MOVW src+4(FP), Rsrc
 	MOVW n+8(FP), Rn
 	MOVW state+12(FP), Rstate
-	MOVW pi+16(FP), Rpi
-	MOVW pj+20(FP), Rpj
+	MOVW i+16(FP), Rpi
+	MOVW j+20(FP), Rpj
 	MOVBU (Rpi), Ri
 	MOVBU (Rpj), Rj
 	MOVW $0, Rk

src/crypto/sha256/sha256block_386.s

@@ -141,7 +141,7 @@
 	MSGSCHEDULE1(index); \
 	SHA256ROUND(index, const, a, b, c, d, e, f, g, h)
 
-TEXT ·block(SB),0,$296-12
+TEXT ·block(SB),0,$296-16
 	MOVL	p_base+4(FP), SI
 	MOVL	p_len+8(FP), DX
 	SHRL	$6, DX