ANDROID: arm64: Use __pa_symbol for kernel symbols

'BACKPORT: arm64: Use __pa_symbol for kernel symbols' missed a spot.
Upstream has removed the fragment associated with idmap_pg_dir, so
this is a 3.18-ony adjustment.

Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Bug: 63737556
Bug: 20045882
Change-Id: If4a65eed30113993e7ac178f69625d5305892184