gdb: migrate i386 and amd64 to the new gdbarch_pseudo_register_write

Make i386 and amd64 use the new gdbarch_pseudo_register_write.  This
fixes writing to pseudo registers in non-current frames for those
architectures.

Change-Id: I4977e8fe12d2cef116f8834c34cdf6fec618554f
Reviewed-By: John Baldwin <jhb@FreeBSD.org>
3 files changed