If /boot/firmware is in fstab, use it as BOOTFS

Debian's raspi-firmware package assumes the boot partition is mounted as
/boot/firmware/ rather than /boot/. This commit adds support for either
approach by default.

rpi-eeprom-update

@@ -29,7 +29,6 @@ FIRMWARE_IMAGE_DIR=${FIRMWARE_IMAGE_DIR:-${FIRMWARE_ROOT}/${FIRMWARE_RELEASE_STA
 FIRMWARE_BACKUP_DIR=${FIRMWARE_BACKUP_DIR:-/var/lib/raspberrypi/bootloader/backup}
 ENABLE_VL805_UPDATES=${ENABLE_VL805_UPDATES:-1}
 RECOVERY_BIN=${RECOVERY_BIN:-${FIRMWARE_ROOT}/${FIRMWARE_RELEASE_STATUS}/recovery.bin}
-BOOTFS=${BOOTFS:-/boot}
 CM4_ENABLE_RPI_EEPROM_UPDATE=${CM4_ENABLE_RPI_EEPROM_UPDATE:-0}
 RPI_EEPROM_UPDATE_CONFIG_TOOL="${RPI_EEPROM_UPDATE_CONFIG_TOOL:-raspi-config}"
 
@@ -576,6 +575,14 @@ findBootFS()
       TMP_BOOTFS_MNT="$(mktemp -d)"
       mount /dev/mmcblk0p1 "${TMP_BOOTFS_MNT}"
       BOOTFS="${TMP_BOOTFS_MNT}"
+   elif [ -z "$BOOTFS" ]; then
+      if ! BOOTFS=$(/usr/lib/raspberrypi-sys-mods/get_fw_loc 2> /dev/null); then
+         for BOOTFS in /boot/firmware /boot; do
+            if findmnt --fstab "$BOOTFS" > /dev/null; then
+               break
+            fi
+         done
+      fi
    fi
 
    # If BOOTFS is not a directory or doesn't contain any .elf files then

rpi-eeprom-update-default

@@ -3,6 +3,8 @@ FIRMWARE_ROOT=/lib/firmware/raspberrypi/bootloader
 FIRMWARE_RELEASE_STATUS="critical"
 FIRMWARE_IMAGE_DIR="${FIRMWARE_ROOT}/${FIRMWARE_RELEASE_STATUS}"
 FIRMWARE_BACKUP_DIR="/var/lib/raspberrypi/bootloader/backup"
-BOOTFS=/boot
 USE_FLASHROM=0
 EEPROM_CONFIG_HOOK=
+
+# BOOTFS can be set here to override auto-detection in rpi-eeprom-update
+#BOOTFS=/boot