Revert "efi_loader: avoid make race condition"

Revert "efi_loader: avoid make race condition"

This reverts commit 2f61b13d6acba787b00598d519c85222e993e4ca.

There is an issue when you build u-boot for arm and then for arm64
without make mrproper between.

Error log:
lib/efi_loader/efi_crt0.o: error adding symbols: File in wrong format
make[2]: *** [lib/efi_loader/helloworld_efi.so] Error 1
rm lib/efi_loader/helloworld.o
make[1]: *** [lib/efi_loader] Error 2
make[1]: *** Waiting for unfinished jobs....

Signed-off-by: Michal Simek <michal.simek@xilinx.com>