gdb: add type::bounds / type::set_bounds

gdb: add type::bounds / type::set_bounds

Add the `bounds` and `set_bounds` methods on `struct type`, in order to
remove the `TYPE_RANGE_DATA` macro.  In this patch, the
`TYPE_RANGE_DATA` macro is changed to use `type::bounds`, so all the
call sites that are used to set a range type's bounds are changed to use
`type::set_bounds`.  The next patch will remove `TYPE_RANGE_DATA`
completely.

gdb/ChangeLog:

	* gdbtypes.h (struct type) <bounds, set_bounds>: New methods.
	(TYPE_RANGE_DATA): Use type::bounds.  Change all uses that
	are used to set the range type's bounds to use set_bounds.

Change-Id: I62e15506239b98404e62bbea8120db184ed87847