aboot: Correct the logic for selecting partition for recovery mode

There is actually msm89xx devices with A/B partition scheme that
has a dedicated recovery partition on the market, even though
Android recommends to remove recovery partition for A/B devices.

It is not related with dynamic partitions at all, dynamic partitions
supports both non-A/B and A/B configurations.

Let's just automatically detect whether if a dedicated recovery
partition is present or not, and use it if it's present.

Author: me-cafebabe

app/aboot/aboot.c

@@ -1658,7 +1658,7 @@ int boot_linux_from_mmc(void)
 	void *vbmeta_image_buf = NULL;
 	uint32_t vbmeta_image_sz = 0;
 #endif
-	char *ptn_name = NULL;
+	char *ptn_name = "boot";
 #if DEVICE_TREE
 	void * image_buf = NULL;
 	unsigned int dtb_size = 0;
@@ -1695,14 +1695,11 @@ int boot_linux_from_mmc(void)
 		goto unified_boot;
 	}
 
-	/* For a/b recovery image code is on boot partition.
-	   If we support multislot, always use boot partition. */
-	if (boot_into_recovery &&
-		((!partition_multislot_is_supported()) ||
-		(target_dynamic_partition_supported())))
+	if (boot_into_recovery) {
+		if (partition_get_index("recovery") != INVALID_PTN) {
 			ptn_name = "recovery";
-	else
-			ptn_name = "boot";
+		}
+	}
 
 retry_boot:
 	index = partition_get_index(ptn_name);