ppc: Zap MHPC board

This board uses eeprom accessors in an incorrect way. The board
is old and unsupported, just zap it.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Tom Rini <trini@ti.com>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Cc: Heiko Schocher <hs@denx.de>