Add Spleen 12x24 and 16x32 on amd64's RAMDISK_CD and arm64 RAMDISK kernels.

Add Spleen 12x24 and 16x32 on amd64's RAMDISK_CD and arm64 RAMDISK kernels.

The size of kernel fonts in RAMDISKs had long been a problem on systems
with large screen resolutions booting via EFI, as previously only the 8x16
font was built into RAMDISKs. As those systems are becoming more common,
this should make the installation and update process more comfortable.

OK deraadt@, jcs@