Makefile: fix (again) EFI part of "symbols: Generate an xen-sym.map

This is a follow-up to commit d14fffcc6a
"fix EFI part of "symbols: Generate an xen-sym.map" which fixed most of
the issues.

However we still have an issue - The file being installed (xen.efi.map)
does not exist in an ARM64 build (the xen.efi is linked againts xen).

The fix can be done two ways:
 a) See if xen.efi.map exists and then copy it
 b) Or link xen.efi.map to xen-syms.map (similar to how xen.efi is linked
    against xen).

The patch chooses the former.

Reported-by: Jan Beulich <JBeulich@suse.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>

xen/Makefile

@@ -67,7 +67,9 @@ _install: $(TARGET)$(CONFIG_XEN_INSTALL_SUFFIX)
 	if [ -r $(TARGET).efi -a -n '$(EFI_DIR)' ]; then \
 		[ -d $(D)$(EFI_DIR) ] || $(INSTALL_DIR) $(D)$(EFI_DIR); \
 		$(INSTALL_DATA) $(TARGET).efi $(D)$(EFI_DIR)/$(T)-$(XEN_FULLVERSION).efi; \
-		$(INSTALL_DATA) $(TARGET).efi.map $(D)$(DEBUG_DIR)/$(T)-$(XEN_FULLVERSION).efi.map; \
+		if [ -e $(TARGET).efi.map ]; then \
+			$(INSTALL_DATA) $(TARGET).efi.map $(D)$(DEBUG_DIR)/$(T)-$(XEN_FULLVERSION).efi.map; \
+		fi; \
 		ln -sf $(T)-$(XEN_FULLVERSION).efi $(D)$(EFI_DIR)/$(T)-$(XEN_VERSION).$(XEN_SUBVERSION).efi; \
 		ln -sf $(T)-$(XEN_FULLVERSION).efi $(D)$(EFI_DIR)/$(T)-$(XEN_VERSION).efi; \
 		ln -sf $(T)-$(XEN_FULLVERSION).efi $(D)$(EFI_DIR)/$(T).efi; \