mb/google/bluey: Rename LB_BOOT_MODE_LOW_BATTERY for clarity

The current LB_BOOT_MODE_LOW_BATTERY actually implies a state where the
battery is below the critical threshold but a charger is attached,
allowing the system to boot into a charging-only or limited state.

Update the enum name to LB_BOOT_MODE_LOW_BATTERY_CHARGING across
coreboot tables and libpayload to better reflect this hardware state.

Changes:
- Rename boot mode enums in commonlib and libpayload.
- Update bluey mainboard logic to use the more descriptive name.
- Refactor is_low_power_boot() to is_low_power_boot_with_charger()
  to improve code readability.
- Ensure the charger-present condition is explicitly checked in
  romstage when setting the boot mode.

TEST=Verify bluey boots into off-mode charging and low-battery
charging modes correctly.

Change-Id: I2478c7519c781a8b5af78445899b7f9bf412cf42
Signed-off-by: Subrata Banik <subratabanik@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/90845
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kapil Porwal <kapilporwal@google.com>
Reviewed-by: Jayvik Desai <jayvik@google.com>

src/commonlib/include/commonlib/coreboot_tables.h

@@ -639,8 +639,11 @@ struct lb_panel_poweroff {
 };
 
 enum boot_mode_t {
+	/* Regular boot scenarios */
 	LB_BOOT_MODE_NORMAL,
-	LB_BOOT_MODE_LOW_BATTERY,
+	/* Device is booting in low-batter w/ charger attached */
+	LB_BOOT_MODE_LOW_BATTERY_CHARGING,
+	/* Device is booting in due to charger insertion */
 	LB_BOOT_MODE_OFFMODE_CHARGING,
 };