Remove PAGE_SIZE call sites.

To enable experiments with non-4KiB page sizes, introduce
an inline page_size() function that will either return the runtime
page size (if PAGE_SIZE is not 4096) or a constant 4096 (elsewhere).
This should ensure that there are no changes to the generated code on
unaffected platforms.

Test: source build/envsetup.sh
      lunch aosp_cf_arm64_16k_phone-userdebug
      m -j32 installclean
      m -j32
Test: launch_cvd \
  -kernel_path /path/to/out/android14-5.15/dist/Image \
  -initramfs_path /path/to/out/android14-5.15/dist/initramfs.img \
  -userdata_format=ext4
Bug: 277272383
Bug: 230790254
Change-Id: Ic0ed98b67f7c6b845804b90a4e16649f2fc94028
diff --git a/linker/linker_main.cpp b/linker/linker_main.cpp
index 26e2228..f7c8ea9 100644
--- a/linker/linker_main.cpp
+++ b/linker/linker_main.cpp
@@ -580,8 +580,8 @@
     }
 
     ElfW(Addr) seg_start = phdr->p_vaddr + si->load_bias;
-    ElfW(Addr) seg_page_end = PAGE_END(seg_start + phdr->p_memsz);
-    ElfW(Addr) seg_file_end = PAGE_END(seg_start + phdr->p_filesz);
+    ElfW(Addr) seg_page_end = page_end(seg_start + phdr->p_memsz);
+    ElfW(Addr) seg_file_end = page_end(seg_start + phdr->p_filesz);
 
     if (seg_page_end > seg_file_end) {
       prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME,