efi_loader: make the UEFI boot manager configurable

Some boards are very tight on the binary size. Booting via UEFI is possible
without using the boot manager.

Provide a configuration option to make the boot manager available.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/include/config_distro_bootcmd.h b/include/config_distro_bootcmd.h
index c986226..2627c2a 100644
--- a/include/config_distro_bootcmd.h
+++ b/include/config_distro_bootcmd.h
@@ -123,14 +123,20 @@
 #endif
 #endif
 
-
-#define BOOTENV_SHARED_EFI                                                \
+#ifdef CONFIG_CMD_BOOTEFI_BOOTMGR
+#define BOOTENV_EFI_BOOTMGR                                               \
 	"boot_efi_bootmgr="                                               \
 		"if fdt addr ${fdt_addr_r}; then "                        \
 			"bootefi bootmgr ${fdt_addr_r};"                  \
 		"else "                                                   \
 			"bootefi bootmgr;"                                \
-		"fi\0"                                                    \
+		"fi\0"
+#else
+#define BOOTENV_EFI_BOOTMGR
+#endif
+
+#define BOOTENV_SHARED_EFI                                                \
+	BOOTENV_EFI_BOOTMGR                                               \
 	\
 	"boot_efi_binary="                                                \
 		"load ${devtype} ${devnum}:${distro_bootpart} "           \