Standardize page property.

ro.boot.hardware.cpu.pagesize is used on some devices to
report the page size. However, we also know what value this
should be from the CPU. Rather than create a separate property
for this, standardize around this property.

This also allows us to test the value of this property on all
devices.

Bug: 358696947
Test: Vts16KPageSizeTest
Change-Id: I7f6260c68e17e7df8a789e9066a7171f3a56f4b0