input: i8042 - Remove special Cayman handling

As of commit 37744fee

 ("sh: remove sh5 support"), support for
the SH5-based Cayman platform can no longer be selected.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Rich Felker <dalias@libc.org>