rl78: Create a flags type for the psw register.

rl78: Create a flags type for the psw register.

For the Renesas rl78 architecture, associate a flags type with the PSW
register. This will cause symbolic flags to be printed when using
the "info registers" command.

gdb/ChangeLog:

	* rl78-tdep.c (struct gdbarch_tdep): Add new field, rl78_psw_type.
	(rl78_register_type): Add case for RL78_PSW_REGNUM.
	(rl78_gdbarch_init): Initialize rl78_psw_type.