berberis: Use berberis::kPageSize

Replace uses of hardcoded kPageSize (4096) with berberis::kPageSize.

Introduce berberis::kMaxPageSize (64KB), which is the max page size of
any supported architecture. This is used to enusre the MmapPool's block
size is a multiple of any supported page size.

Bug: 315325080
Test: lunch cf_x86_64_phone-trunk_staging-userdebug && m && launch_cvd
Test: atest -c berberis_host_tests
Test: atest -c berberis_ndk_program_tests
Test: atest -c berberis_ndk_program_tests_static
Test: atest -c ndk_program_tests
Test: atest -c ndk_program_tests_static
Change-Id: I371a36d01d5bb19db5ec61182d8f70f8fd7f0a63
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>