gdb: add inferior parameter to breakpoint_init_inferior

By inspection, I believe that breakpoint_init_inferior doesn't call
anything that relies on the current program space or inferior.  So,
add an inferior parameter, to make the current inferior / program space
references bubble up one level.

Change-Id: Ib07b7a6d360e324f6ae1aa502dd314b8cce421b7
Approved-By: Andrew Burgess <aburgess@redhat.com>