sh: change PVR of SH7757 for 2nd cut

All 1st cut silicon in the wild has been replaced by the 2nd cut, so it's
safe to replace all of the 1st cut references and support.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>