mb/google/bluey: Use SOC PMIC API to detect off-mode charging event

Refactor the is_off_mode() detection API on the Bluey mainboard
to call the newly introduced SOC-specific PMIC function,
is_pon_on_ac().

This change delegates the complex Power-On (PON) log parsing and
PMIC register checking to the SOC layer, simplifying the mainboard
code base. The board layer now contains only the high-level policy
wrapper for detecting cable-power-on events.

This improves modularity and ensures the board code relies on the
correct hardware abstraction.

Key changes:
- Implement is_off_mode() as a simple wrapper around is_pon_on_ac()
  (from the SOC PMIC library).
- Include soc/pmic.h to access the SOC's PMIC APIs.
- Expose is_off_mode() in board.h.

BUG=b:439819922
TEST=Verify boot mode on Google/Quenbi.

Change-Id: Ibc13c3ad96846cf5b3fb9bcf461e3f338ac9b8bd
Signed-off-by: Kapil Porwal <kapilporwal@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/89122
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Subrata Banik <subratabanik@google.com>

src/mainboard/google/bluey/board.h

@@ -41,6 +41,7 @@
 #endif
 
 void setup_chromeos_gpios(void);
+bool is_off_mode(void);
 void enable_slow_battery_charging(void);
 void disable_slow_battery_charging(void);
 

src/mainboard/google/bluey/charging.c

@@ -1,7 +1,9 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
 #include "board.h"
+#include <soc/pmic.h>
 #include <soc/qcom_spmi.h>
+#include <types.h>
 
 #define SMB1_SLAVE_ID 0x07
 #define SMB2_SLAVE_ID 0x0A
@@ -41,3 +43,19 @@ void disable_slow_battery_charging(void)
 	spmi_write8(SMB1_CHGR_CHRG_EN_CMD, CHRG_DISABLE);
 	spmi_write8(SMB2_CHGR_CHRG_EN_CMD, CHRG_DISABLE);
 }
+
+/*
+ * is_off_mode - Check if the system is booting due to an off-mode power event.
+ *
+ * This function provides the board-level policy wrapper for detecting if the
+ * system power-on was triggered by an external charging event (e.g., cable
+ * insertion). This is typically used to enter LB_BOOT_MODE_OFFMODE_CHARGING.
+ *
+ * @return true if the system was triggered by a specific off-mode reason
+ * (e.g., charging cable insertion).
+ * @return false otherwise.
+ */
+bool is_off_mode(void)
+{
+	return is_pon_on_ac();
+}