ARC: gdbserver using regset interface possibly broken

ptrace regset interface relies on ELF_NGREG for ceiling the size of user
request. So any larger request (even if legit)  would be clipped.

The existing def of ELF_NGREG didn't use user_regs_struct and was
technically one placeholder short (stop_pc) - although the current code
would still work because pt_regs includes a bunch of extra fields,
making
      ELF_NGREG >= sizeof(struct user_regs_struct)/sizeof(long)

But we need to remove this ambiguity, specially since pt_regs should NOT
be directly associated with with anything userspace-ish.
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

arch/arc/include/asm/elf.h

@@ -27,11 +27,7 @@
 typedef unsigned long elf_greg_t;
 typedef unsigned long elf_fpregset_t;
 
-
-/* core dump regs is in the order pt_regs, callee_regs, stop_pc (for gdb) */
-#define ELF_NGREG	((sizeof(struct pt_regs) + sizeof(struct callee_regs) \
-			  + sizeof(unsigned long)) / sizeof(elf_greg_t))
-
+#define ELF_NGREG	(sizeof(struct user_regs_struct) / sizeof(elf_greg_t))
 typedef elf_greg_t elf_gregset_t[ELF_NGREG];
 
 /*