Make sure we're playing with integral modes before call extract_integral_bit_field.

gcc/ChangeLog:

	* expmed.c (extract_bit_field_1): Make sure we're playing with
	integral modes before call extract_integral_bit_field.
	(extract_integral_bit_field): Add a parameter of type
	scalar_int_mode which corresponds to of tmode.
	And call extract_and_convert_fixed_bit_field instead of
	extract_fixed_bit_field and convert_extracted_bit_field.
	(extract_and_convert_fixed_bit_field): New function, it's a
	combination of extract_fixed_bit_field and
	convert_extracted_bit_field.