efi_loader: support building UEFI binaries on sandbox

On the sandbox the UEFI binaries must match the host architectures.

Adjust the Makefiles. Provide the PE/COFF header and relocation files.

Allow building helloworld.efi on the sandbox.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/lib/efi_loader/Makefile b/lib/efi_loader/Makefile
index 01769ea..7db4060 100644
--- a/lib/efi_loader/Makefile
+++ b/lib/efi_loader/Makefile
@@ -6,6 +6,9 @@
 # This file only gets included with CONFIG_EFI_LOADER set, so all
 # object inclusion implicitly depends on it
 
+asflags-y += -DHOST_ARCH="$(HOST_ARCH)"
+ccflags-y += -DHOST_ARCH="$(HOST_ARCH)"
+
 CFLAGS_efi_boottime.o += \
   -DFW_VERSION="0x$(VERSION)" \
   -DFW_PATCHLEVEL="0x$(PATCHLEVEL)"