ANDROID: mm: Set PAGE_BLOCK_ORDER to 8 when ARM64_16K_PAGES

This config will allow the 16kb page size kernels to have the
same CMA_MIN_ALIGNMENT_BYTES that 4k kernels. This means that
the CMA configs for the drivers won't have to change.

Note: This change is needed to avoid breaking old kernel
builds.

Bug: 424212284
Bug: 375647879
Bug: 355449177
Bug: 418282543
Test: tools/bazel run //common:kernel_aarch64_dist
      tools/bazel run //common:kernel_aarch64_16k_dist
      tools/bazel run //common:kernel_x86_64_dist
Change-Id: Icbfcab0d7e5ba18b3fc35c1186ef79e82f3e7ab1
Signed-off-by: Juan Yescas <jyescas@google.com>

mm/Kconfig

diff --git a/mm/Kconfig b/mm/Kconfig
index 4b97eb0..0bf806c0 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -929,6 +929,13 @@
 	int
 
 #
+# Select this config option from the ARM64 architecture Kconfig to set
+# the page size to 16KB.
+# See b/424212284 for more information.
+config ARM64_16K_PAGES
+	bool
+
+#
 # When ARCH_FORCE_MAX_ORDER is not defined,
 # the default page block order is MAX_ORDER (10) as per
 # include/linux/mmzone.h.
@@ -937,6 +944,7 @@
 	int "Page Block Order"
 	range 1 10 if ARCH_FORCE_MAX_ORDER = 0 || ARCH_FORCE_MAX_ORDER = ""
 	default 10 if ARCH_FORCE_MAX_ORDER = 0 || ARCH_FORCE_MAX_ORDER = ""
+	default 8 if ARM64_16K_PAGES
 	range 1 ARCH_FORCE_MAX_ORDER if ARCH_FORCE_MAX_ORDER != 0
 	default ARCH_FORCE_MAX_ORDER if ARCH_FORCE_MAX_ORDER != 0
 	help