ANDROID: 16K: Only support page size emulation for x86_64

The original intention was to keep this generic so that it can be
used for other architectures (arm64).

This is no longer needed, only emulate PAGE_SHIFT for x86_64.

Bug: 328138888
Bug: 345252092
Bug: 315325080
Bug: 302403436
Change-Id: Ie1fb9b8cf6a18de77b2ec615ba5452060216c483
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>