powerpc: Shrink ULPs for float128

During the development of float128 on powerpc64le, the ulps have been
generated since early versions of the patches.  On those versions, the
functions gamma and pow10 were mistakenly thought to be part of the API.
After review, the functions were removed, however the ulps for them were
carried in the ulps file.

This patch removes such entries from the ulps file, as well as it
shrinks the ulps for the cpow and lgamma functions.

Tested for powerpc64le.

	* sysdeps/powerpc/fpu/libm-test-ulps: Update.