efi_loader: default EFI_LOADER=n on ARM11

Some of the ARM11 boards have tight limits on the size of U-Boots. Hence
use EFI_LOADER=n as default on ARM11.

Set EFI_LOADER=y for the Raspberry Pi and Raspberry Pi Zero as these boards
have sufficient storage on the SD card.

Suggested-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>