Add support for E7505 northbridge.

Adapted from northbridge/intel/e7501 with only minor changes.
This commit provides minimal patch from e7501 and I prefer any
cosmetic clean-up to be done after initial merge.

Due the incomplete register specifications, it is safer to have
e7505 as a separate directory in case I improve it to support
wider range of memory configurations. I have no e7501 to test with.

Change-Id: Iba3bf9d69ff5e9d9ef3a6ebf8259f048c55d637d
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/295
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>