rx: Create and use flags types for psw, bpsw, and fpsw registers.

rx: Create and use flags types for psw, bpsw, and fpsw registers.

This change adds two flags types for the (Renesas RX) psw, bpsw, and
fpsw registers.  As a result, symbolic flags are displayed for these
registers in the output of GDB's "info registers" command as well as
in output from other commands, such as "print".

gdb/ChangeLog:

	* rx-tdep.c (RX_BPSW_REGNUM, RX_FPSW_REGNUM): New constants.
	(struct gdbarch_tdep): Add fields rx_psw_type and rx_fpsw_type.
	(rx_register_type): Add cases for RX_PSW_REGNUM, RX_BPSW_REGNUM,
	and RX_FPSW_REGNUM.
	(rx_gdbarch_init): Initialize PSW, BPSW, and FPSW flags types.