sh: add support for ax88796 and 93cx6 to highlander boards

This patch adds support for the ax88796 driver on highlander boards.

Implemented using the 93cx6 EEPROM support introduced by commit-id
89e536a1.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>