asm-generic/ptrace.h: start a common low level ptrace helper

This is a series of low level ptrace unification steps to make it easier
for common code (like KGDB) to poke at register state.  This also avoids
having to duplicate higher level operations for most ports which don't
have special needs for accessing things.

This patch:

This implements a bunch of helper funcs for poking the registers of a
ptrace structure.  Now common code should be able to portably update
specific registers (like kgdb updating the PC).

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Jason Wessel <jason.wessel@windriver.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Sergei Shtylyov <sshtylyov@mvista.com>
Cc: Dongdong Deng <dongdong.deng@windriver.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>