gdb: move frame_info_ptr to frame.{c,h}

gdb: move frame_info_ptr to frame.{c,h}

A patch later in this series will make frame_info_ptr access some
fields internal to frame_info, which we don't want to expose outside of
frame.c.  Move the frame_info_ptr class to frame.h, and the definitions
to frame.c.  Remove frame-info.c and frame-info.h.

Change-Id: Ic5949759e6262ea0da6123858702d48fe5673fea
Reviewed-By: Bruno Larsen <blarsen@redhat.com>