powerpc/mpc8308: fix USB DR controller initialization

MPC8308 has ULPI pin muxing settings in SICRH register, bits 17-18
which is different from both MPC8313 and MPC8315.
Also MPC8308 doesn't have REFSEL, UTMI_PHY_EN and OTG_PORT fields
in the USB DR controller CONTROL register.

Signed-off-by: Ilya Yanok <yanok@emcraft.com>
Tested-by: Wolfgang Denk <wd@denx.de>
Acked-by: Wolfgang Denk <wd@denx.de>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>