Implement vt_vbefb to support Vesa Bios Extensions (VBE) framebuffer with VT. vt_vbefb is
built based on vt_efifb and is assuming similar data for initialization.
Therefore we can use the struct efi_fb, but with added field fb_bpp for
depth (UEFI is only supporting 32-bit depth and was not needing it) and we
use MODINFOMD_VBE_FB to identify the structure in kernel metadata.
struct efi_fb, is populated by boot loader, and is passed to kernel via metadata payload.