Add CONFIG_NO_GFX_INIT=y to T440p board

[srgrint]

This PR adds CONFIG_NO_GFX_INIT=y to the T440p coreboot configuration, leaving graphics init exclusively to the heads kernel.

There are 3 benefits of this change:

• Reduces the size of the ramstage
• Decreases boot time
• Likely improves security by reducing size of the trusted code base and hence attack surface

Have tested on my intel only T440p and seems to work fine.

Further discussed in #1323

[tlaurion]

Merged upstream with 6d0cd94
being part of #1378

https://github.com/osresearch/heads/blob/ab1faf5389dbfbc174e3cbf6cdec0be1cba14772/config/coreboot-t440p.config#L16