New generic log2f

New generic log2f

Similar to the new logf: double precision arithmetics and a small
lookup table is used. The argument reduction step is the same as in
the new logf.

without wrapper on aarch64:
log2f reciprocal-throughput: 2.3x faster
log2f latency: 2.1x faster
old worst case error: 1.72 ulp
new worst case error: 0.75 ulp
aarch64 .text size: -252 bytes
aarch64 .rodata size: +244 bytes

	* math/Makefile (type-float-routines): Add e_log2f_data.
	* sysdeps/ieee754/flt-32/e_log2f.c: New implementation.
	* sysdeps/ieee754/flt-32/e_log2f_data.c: New file.
	* sysdeps/ieee754/flt-32/math_config.h (__log2f_data): Define.
	(LOG2F_TABLE_BITS, LOG2F_POLY_ORDER): Define.
	* sysdeps/i386/fpu/e_log2f_data.c: New file.
	* sysdeps/ia64/fpu/e_log2f_data.c: New file.
	* sysdeps/m68k/m680x0/fpu/e_log2f_data.c: New file.