Target FP printing: Use floatformat_to_string in tdep code

Target FP printing: Use floatformat_to_string in tdep code

A few tdep files use target-specific printing routines to output values in
the floating-point registers.  To get rid of host floating-point code,
this patch changes them to use floatformat_to_string instead.

No functional change intended, the resulting output should look the same.

ChangeLog:
2017-10-24  Ulrich Weigand  <uweigand@de.ibm.com>

	* i387-tdep.c (print_i387_value): Use floatformat_to_string.
	* sh64-tdep.c (sh64_do_fp_register): Likewise.
	* mips-tdep.c (mips_print_fp_register): Likewise.