efi_loader: fix EFI entry counting

`bootefi selftest` fails on qemu-x86_defconfig if efi_selftest() is not
invoked using EFI_CALL().

Likewise we call the entry point of EFI payloads with
EFI_CALL(efi_start_image()).

entry_count indicates if we are in U-Boot (1) or in EFI payload code (0).
As we start in U-Boot code the initial value has to be 1.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>