s390/diag: Move diag.c to diag specific folder

Move implementation of s390 diagnose code to diag specific folder.

Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

arch/s390/kernel/Makefile

@@ -38,7 +38,7 @@ CFLAGS_unwind_bc.o	+= -fno-optimize-sibling-calls
 
 obj-y	:= head64.o traps.o time.o process.o early.o setup.o idle.o vtime.o
 obj-y	+= processor.o syscall.o ptrace.o signal.o cpcmd.o ebcdic.o nmi.o
-obj-y	+= debug.o irq.o ipl.o dis.o diag.o vdso.o cpufeature.o
+obj-y	+= debug.o irq.o ipl.o dis.o vdso.o cpufeature.o
 obj-y	+= sysinfo.o lgr.o os_info.o ctlreg.o
 obj-y	+= runtime_instr.o cache.o fpu.o dumpstack.o guarded_storage.o sthyi.o
 obj-y	+= entry.o reipl.o kdebugfs.o alternative.o