[build] Allow for 32-bit and 64-bit versions of util/zbin

Parsing ELF data is simpler if we don't have to build a single binary
to handle both 32-bit and 64-bit ELF formats.

Allow for separate 32-bit and 64-bit binaries built from util/zbin.c
(as is already done for util/elf2efi.c).

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/Makefile

@@ -45,7 +45,8 @@ SORTOBJDUMP	:= ./util/sortobjdump.pl
 PADIMG		:= ./util/padimg.pl
 LICENCE		:= ./util/licence.pl
 NRV2B		:= ./util/nrv2b
-ZBIN		:= ./util/zbin
+ZBIN32		:= ./util/zbin32
+ZBIN64		:= ./util/zbin64
 ELF2EFI32	:= ./util/elf2efi32
 ELF2EFI64	:= ./util/elf2efi64
 EFIROM		:= ./util/efirom