mb/lenovo/t400: use socket mPGA478MN instead of BGA945

The T400 features a socket P (mPGA478MN) and could potentially support
model_6fx CPUs.

Change-Id: I24f3356aa213c29011953daed31f46404e7a4d9d
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/17155
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>
2 files changed