Apply cache-as-ram conditionally on socket mPGA604

Apply cache-as-ram conditionally on socket mPGA604

The socket mPGA604 is for P4 Xeon which to my knowledge is always
HT-enabled. I assume the existing usage of car/cache_as_ram.inc
on socket_mPGA604, namely the Tyan S2735, as broken.

Existing car/cache_as_ram.inc has invalid SIPI vector and it does
not initialise AP CPU's to activate L2 cache.

Other mPGA604 boards are not affected, as they have not been
converted to CAR.

Change-Id: I7320589695c7f6a695b313a8d0b01b6b1cafbb04
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/607
Tested-by: build bot (Jenkins)
Reviewed-by: Idwer Vollering <vidwer@gmail.com>
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>