Prepare the manual to display math errors for float128 functions

When float128 support gets enabled for powerpc64le, the ULP errors for
float128 functions need to be presented in the manual.  This patch adds
support for displaying them.

Tested for powerpc64le and s390x.

	* manual/libm-err-tab.pl (@all_floats, %suffices, parse_ulps):
	Enable generation of float128 entries on the error table.