efiboot on armv7/arm64

[Jared McNeill <jmcneill%invisible.ca@localhost>]

Hi folks --

I've added 32-bit EFI booting support, and switched armv7.img over to use 
it -- now armv7 and arm64 boot the same way.

So the layout on disk looks like this:

  /boot/				<-- FAT partition
  /boot/EFI/BOOT/bootarm.efi		<-- armv7 NetBSD bootloader
  /boot/EFI/BOOT/bootaa64.efi		<-- arm64 NetBSD bootloader
  /boot/dtb/${fdtfile}			<-- board specific FDT file
  /netbsd				<-- ELF NetBSD kernel

To use this, your U-Boot has to be fairly recent (2018.05 and later works 
well). You can confirm that your U-Boot supports EFI services by the 
presence of a "bootefi" command.

Cheers,
Jared