gdb: make symbol_found_callback_ftype a function_view

All uses of symbol_found_callback_ftype use it within a function_view,
so factor out the function_view into the type alias.

Change-Id: I24a1d2fc233aa5d593c9c68581a9912bfee3a348
Approved-By: Andrew Burgess <aburgess@redhat.com>
5 files changed