scripts/decodecode: add support for LoongArch

An example how to invoke decodecode for loongarch64:
$ echo 'Code: 380839f6 380831f9 28412bae <24000ca6>
004081ad 0014cb50 004083e8 02bff34c 58008e91' | \
ARCH=loongarch CROSS_COMPILE=loongarch64-linux-gnu- \
./scripts/decodecode
Code: 380839f6 380831f9 28412bae <24000ca6> 004081ad 0014cb50 004083e8 02bff34c 58008e91
All code
========
0: 380839f6 ldx.w $fp, $t3, $t2
4: 380831f9 ldx.w $s2, $t3, $t0
8: 28412bae ld.h $t2, $s6, 74(0x4a)
c:* 24000ca6 ldptr.w $a2, $a1, 12(0xc) <-- trapping instruction
10: 004081ad slli.w $t1, $t1, 0x0
14: 0014cb50 and $t4, $s3, $t6
18: 004083e8 slli.w $a4, $s8, 0x0
1c: 02bff34c addi.w $t0, $s3, -4(0xffc)
20: 58008e91 beq $t8, $t5, 140(0x8c) # 0xac

Code starting with the faulting instruction
===========================================
0: 24000ca6 ldptr.w $a2, $a1, 12(0xc)
4: 004081ad slli.w $t1, $t1, 0x0
8: 0014cb50 and $t4, $s3, $t6
c: 004083e8 slli.w $a4, $s8, 0x0
10: 02bff34c addi.w $t0, $s3, -4(0xffc)
14: 58008e91 beq $t8, $t5, 140(0x8c) # 0xa0

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Youling Tang <[e-mail]>
Acked-by: Huacai Chen <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

scripts/decodecode

···
     case `uname -m` in
 	aarch64*) ARCH=arm64 ;;
 	arm*) ARCH=arm ;;
+	loongarch*) ARCH=loongarch ;;
     esac
 fi
 
···
 
 	if [ "$ARCH" = "riscv" ]; then
 		OBJDUMPFLAGS="-M no-aliases --section=.text -D"
+		${CROSS_COMPILE}strip $t.o
+	fi
+
+	if [ "$ARCH" = "loongarch" ]; then
 		${CROSS_COMPILE}strip $t.o
 	fi