efi_loader: split efi_init_obj_list() into two stages

In the next commit, CONFIG_EFI_SETUP_EARLY will become mandated
in order to support dynamic enumeration of efi_disk objects.

This can, however, be problematic particularly in case of file-based
variable storage (efi_variable.c, default).
Non-volatile variables are to be restored from EFI system partition
by efi_init_variables() in efi_init_obj_list(). When efi_init_obj_list()
is called in board_init_r(), we don't know yet what disk devices
we have since none of device probing commands (say, scsi rescan) has not
been executed at that stage.

So in this commit, a preparatory change is made; efi_init_obj_list() is
broken into the two functions;
   * efi_init_early(), and
   * new efi_init_obj_list()

Only efi_init_early() will be called in board_init_r(), which allows
us to execute any of device probing commands, either though "preboot"
variable or normal command line, before calling efi_init_obj_list() which
is to be invoked at the first execution of an efi-related command
(or at efi_launch_capsules()) as used to be.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>

include/efi_loader.h

@@ -493,6 +493,8 @@ struct efi_register_notify_event {
 /* List of all events registered by RegisterProtocolNotify() */
 extern struct list_head efi_register_notify_events;
 
+/* called at pre-initialization */
+int efi_init_early(void);
 /* Initialize efi execution environment */
 efi_status_t efi_init_obj_list(void);
 /* Install device tree */