{drivers, lib}: Move low-battery user notification logic outside FSP

This patch refactors low-battery user notification logic (Kconfig,
APIs to check if low-battery rendering is required, low-battery
shutdown is required) outside FSP driver code to ensure in future
non-FSP platforms might still be able to leverage this feature/logics
to render the low-battery indicator icon during boot.

Specifically, it:

- Moves Kconfig options related to low-battery notifications from
  drivers/intel/fsp to lib/
- Relocates the low-battery check and shutdown APIs drivers/intel/fsp
  to bootsplash.h
* Adjusts the vendor driver to utilize the new APIs for low-battery
  rendering decisions.
* Drop the unwanted header file "fsp/api.h" from bmp_logo.c

This change avoids tight coupling of low-battery functionality to FSP,
promoting code reusability across platforms.

BUG=b:400738815
TEST=Able to build and boot google/brox.

Change-Id: Iaa730dac2bb4866183408b6390221f0bb8411a48
Signed-off-by: Subrata Banik <subratabanik@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/86756
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kapil Porwal <kapilporwal@google.com>

src/vendorcode/google/chromeos/battery.c

@@ -1,7 +1,7 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
 #include <ec/google/chromeec/ec.h>
-#include <fsp/api.h>
+#include <bootsplash.h>
 
 /*
  * Check if low battery shutdown is needed