efi_loader: installation of EFI_RNG_PROTOCOL

Having an EFI_RNG_PROTOCOL without a backing RNG device leads to failure
to boot Linux 5.8.

Only install the EFI_RNG_PROTOCOL if we have a RNG device.

Reported-by: Scott K Logan <logans@cottsay.net>
Cc: Neil Armstrong <narmstrong@baylibre.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

lib/efi_loader/efi_setup.c

@@ -151,6 +151,11 @@ efi_status_t efi_init_obj_list(void)
 	if (ret != EFI_SUCCESS)
 		goto out;
 #endif
+	if (IS_ENABLED(CONFIG_EFI_RNG_PROTOCOL)) {
+		ret = efi_rng_register();
+		if (ret != EFI_SUCCESS)
+			goto out;
+	}
 	/* Initialize variable services */
 	ret = efi_init_variables();
 	if (ret != EFI_SUCCESS)