cpu/amd/model_10xxx: Move GFXUMA size calculation to separate function

This is required for early CBMEM support.

Change-Id: I31d9b6a04ef963a7d3e045d9c5201ae64604218a
Signed-off-by: Timothy Pearson <tpearson@raptorengineeringinc.com>
Reviewed-on: http://review.coreboot.org/8663
Tested-by: build bot (Jenkins)
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
4 files changed