For testing we need to build some ELF files containing binman symbols. Add
these to the Makefile and check in the binaries:

u_boot_binman_syms - normal, valid ELF file
u_boot_binman_syms_bad - missing the __image_copy_start symbol
u_boot_binman_syms_size - has a binman symbol with an invalid size

Signed-off-by: Simon Glass