sh: Add sh4 fpu Implies folder

The commit 605f3817 (sh: Split BE/LE abilist) did not take in
consideration the SH4 fpu support.

Checked with a build for sh4-linux-gnu and manually checked that
the implementations at sysdeps/sh/sh4/fpu/ are selected.

John Paul Adrian Glaubitz also confirmed it fixes the build issues
he encontered.

(cherry-picked from 9ff2674e)