efi_loader: Enable run-time variable support for tee based variables

We recently added functions for storing/restoring variables
from a file to a memory backed buffer marked as __efi_runtime_data
commit f1f990a8c9 ("efi_loader: memory buffer for variables")
commit 5f7dcf079d ("efi_loader: UEFI variable persistence")

Using the same idea we now can support GetVariable() and GetNextVariable()
on the OP-TEE based variables as well.

So let's re-arrange the code a bit and move the commmon code for
accessing variables out of efi_variable.c. Create common functions for
reading variables from memory that both implementations can use on
run-time. Then just use those functions in the run-time variants of the
OP-TEE based EFI variable implementation and initialize the memory
buffer on ExitBootServices()

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

lib/efi_loader/efi_var_common.c

@@ -166,6 +166,28 @@ efi_status_t EFIAPI efi_query_variable_info(
 	return EFI_EXIT(ret);
 }
 
+efi_status_t __efi_runtime EFIAPI
+efi_get_variable_runtime(u16 *variable_name, const efi_guid_t *guid,
+			 u32 *attributes, efi_uintn_t *data_size, void *data)
+{
+	efi_status_t ret;
+
+	ret = efi_get_variable_mem(variable_name, guid, attributes, data_size, data, NULL);
+
+	/* Remove EFI_VARIABLE_READ_ONLY flag */
+	if (attributes)
+		*attributes &= EFI_VARIABLE_MASK;
+
+	return ret;
+}
+
+efi_status_t __efi_runtime EFIAPI
+efi_get_next_variable_name_runtime(efi_uintn_t *variable_name_size,
+				   u16 *variable_name, efi_guid_t *guid)
+{
+	return efi_get_next_variable_name_mem(variable_name_size, variable_name, guid);
+}
+
 /**
  * efi_set_secure_state - modify secure boot state variables
  * @secure_boot:	value of SecureBoot