Introduce enum_flag type for ui_out flags

Introduce enum_flag type for ui_out flags

This patch changes the ui_out flags to be an enum flag.

gdb/ChangeLog:

	* ui-out.h: Include "common/enum-flags.h".
	(enum ui_flags): Rename to ...
	(enum ui_out_flag): ... this.
	(ui_out_flags): Define enum flag type.
	(ui_out_test_flags): Change type of parameter to ui_out_flags.
	(ui_out_new): Likewise.
	* ui-out.c (ui_out_test_flags): Likewise.
	(ui_out_new): Likewise.
	* cli-out.c (cli_out_new): Update variable type.
	* mi/mi-out.c (mi_out_new): Likewise.
	* tui/tui-out.c (tui_out_new): Likewise.