sh: Handle SH-4 FPU variants with broken CVR values.

Usually we can look to the CVR to work out whether we have an FPU or not.
Unfortunately not all parts comply with this, so just set the flag
manually for all SH-4 parts and clear it on the only SH-4 that doesn't
have one (SH4-501).

Signed-off-by: Paul Mundt <lethal@linux-sh.org>