Make squashfs sparse image generation optional

Allow non-sparse squashfs image generation, a la ext filesystems.

Bug: 26218766
Change-Id: Ifd596af16411e0cf69a2e7e05d725fd9442dc79c
diff --git a/core/Makefile b/core/Makefile
index 301e8b2..18e01f9 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -728,6 +728,9 @@
 endif
 endif
 
+ifneq (true,$(TARGET_USERIMAGES_SPARSE_SQUASHFS_DISABLED))
+  INTERNAL_USERIMAGES_SPARSE_SQUASHFS_FLAG := -s
+endif
 ifeq ($(BOARD_SYSTEMIMAGE_FILE_SYSTEM_TYPE),squashfs)
 INTERNAL_USERIMAGES_DEPS += $(MAKE_SQUASHFS) $(MKSQUASHFSUSERIMG) $(IMG2SIMG)
 endif
@@ -764,6 +767,7 @@
 $(if $(BOARD_OEMIMAGE_PARTITION_SIZE),$(hide) echo "oem_size=$(BOARD_OEMIMAGE_PARTITION_SIZE)" >> $(1))
 $(if $(BOARD_OEMIMAGE_JOURNAL_SIZE),$(hide) echo "oem_journal_size=$(BOARD_OEMIMAGE_JOURNAL_SIZE)" >> $(1))
 $(if $(INTERNAL_USERIMAGES_SPARSE_EXT_FLAG),$(hide) echo "extfs_sparse_flag=$(INTERNAL_USERIMAGES_SPARSE_EXT_FLAG)" >> $(1))
+$(if $(INTERNAL_USERIMAGES_SPARSE_SQUASHFS_FLAG),$(hide) echo "squashfs_sparse_flag=$(INTERNAL_USERIMAGES_SPARSE_SQUASHFS_FLAG)" >> $(1))
 $(hide) echo "selinux_fc=$(SELINUX_FC)" >> $(1)
 $(if $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_SUPPORTS_BOOT_SIGNER),$(hide) echo "boot_signer=$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_SUPPORTS_BOOT_SIGNER)" >> $(1))
 $(if $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_SUPPORTS_VERITY),$(hide) echo "verity=$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_SUPPORTS_VERITY)" >> $(1))