protocan-boot: support single-slot targets

c/protocan-boot/include/pcan_boot.h

@@ -79,6 +79,10 @@ typedef struct {
     uint8_t hardware_revision;
     uint32_t firmware_version;
     uint8_t active_slot;
+    /** 1 for an in-place/single-slot target, 2 for A/B. Zero keeps legacy A/B. */
+    uint8_t slot_count;
+    /** Writable image capacity. Zero uses PCAN_BOOT_SLOT_SIZE. */
+    uint32_t max_image_size;
     uint8_t ack_window; /**< 1 — ACK каждого блока, 16 — ACK каждых 16 блоков. */
 } pcan_boot_config_t;