Disable vga if EFI framebuffer present. vt(9) should handle this internally
based on efifb's higher priority, but it doesn't, and this at least lets
us build a kernel that boots on both BIOS and EFI systems for now.
Move up fibnum to ensure it is always defined.

Found by:	ian
MFC with:	r264987
Increase the maximum framebuffer size to more reasonable values reflecting
the high-resolution boot consoles present on Open Firmware and EFI systems.