libvulkan: Remove use of hardcoded PAGE_SIZE 4096

bionic hard codes the PAGE_SIZE macro as 4096. This is going away as
Android begins to support larger page sizes. Remove the usage of this
assumption from libvulkan source; use instead getpagesize() which
provides the real pagesize.

Test: mma
Bug: 295227858
Change-Id: Ie7c2c2f47d8c61c7495dbd3d88bb63ccf7a74063
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>