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/cmd/Kconfig b/cmd/Kconfig
index 99b8a0e..cf982ff 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -320,7 +320,7 @@
 
 config CMD_BOOTEFI_HELLO_COMPILE
 	bool "Compile a standard EFI hello world binary for testing"
-	depends on CMD_BOOTEFI && !CPU_V7M && !SANDBOX
+	depends on CMD_BOOTEFI && !CPU_V7M
 	default y
 	help
 	  This compiles a standard EFI hello world application with U-Boot so