efi_loader: set load options in boot manager

Up to now we used the value of the bootargs environment variable as load
options in the boot manager. This is not correct. The data has to be taken
from the Boot#### variable.

Let the boot manager copy the optional data of the EFI_LOAD_OPTION as load
options to the loaded image protocol.

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