gdb/jit: move cached_code_address and jit_breakpoint to jiter_objfile_data

gdb/jit: move cached_code_address and jit_breakpoint to jiter_objfile_data

This is in preparation for allowing more than one JITer objfile per
program space.  Once we do that, each JITer objfile will have its own
JIT breakpoint (on the __jit_debug_register_code function it provides).
The cached_code_address field is just the runtime / relocated address of
that symbol.

Since they are going to become JITer-objfile-specific and not
program-space-specific, move these fields from jit_program_space_data to
jiter_objfile_data.

gdb/ChangeLog:
2020-07-22  Simon Marchi  <simon.marchi@polymtl.ca>

	* jit.h (struct jiter_objfile_data) <cached_code_address,
	jit_breakpoint>: Move to here from ...
	* jit.c (jit_program_space_data): ... here.
	(jiter_objfile_data::~jiter_objfile_data): Update.
	(jit_breakpoint_deleted): Update.
	(jit_breakpoint_re_set_internal): Update.