efi_loader: the development target should be the EBBR

efi_loader: the development target should be the EBBR

Two subsets of the UEFI specifications have been defined. The one for
servers is "Server Base Boot Requirements System Software on ARM
Platforms" (SBBR), the one for embedded systems is the "Embedded Base Boot
Requirements (EBBR) Specification". Reaching compliance with thei EBBR is a
more realistic development target than reaching complicance with the SBBR.

Suggested-by: Alexander Graf <agraf@csgraf.de>
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>