s390/decompressor: correct some asm symbols annotations

s390/decompressor: correct some asm symbols annotations

Use SYM_CODE_* annotations for asm functions, so that function lengths
are recognized correctly.

Also currently the most part of startup is marked as startup_kdump. Move
misplaced startup_kdump where it belongs.

$ nm -n -S arch/s390/boot/compressed/vmlinux
Before:
0000000000010000 T startup
0000000000010010 T startup_kdump
After:
0000000000010000 0000000000000014 T startup
0000000000010014 00000000000000b0 t startup_normal
0000000000010180 00000000000000b2 t startup_kdump

Reviewed-by: Alexander Egorenkov <egorenar@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>