Rename APEX Namespace

Rename APEX Namespace

Current APEX Namespace is named with APEX name itself, which also uses
.(dot) so linker configuration can keep the syntax safe. Update name of
namespace from APEX by replacing '_' with '.' so keep configuration safe
for future syntax update.

Bug: 148826508
Test: m -j passed
Test: boot succeeded from cuttlefish and walleye
Change-Id: I9185c909678e2e39d539622d51d8f378b819b466