BoardConfigCommon.mk& fstab.ramdisk.common: update for product partition

update to use dynamic product partition, as it's mandatory now
by the commit here:
https://android-review.googlesource.com/c/platform/system/core/+/1264148

otherwise it will failed to boot to home screen successfully

Test: db845c boot to home screen successfully

Signed-off-by: Yongqin Liu <yongqin.liu@linaro.org>
Change-Id: Ib777b7006ef3b46fcf93c85d301ab83e1f2f61bd
diff --git a/fstab.ramdisk.common b/fstab.ramdisk.common
index a2dcc4c..9554d4e 100644
--- a/fstab.ramdisk.common
+++ b/fstab.ramdisk.common
@@ -1,3 +1,4 @@
 system		/system		ext4	noatime,ro,errors=panic		wait,logical,first_stage_mount
 vendor		/vendor		ext4	noatime,ro,errors=panic		wait,logical,first_stage_mount
 system_ext	/system_ext	ext4	noatime,ro,errors=panic		wait,logical,first_stage_mount
+product	/product	ext4	noatime,ro,errors=panic		wait,logical,first_stage_mount