arm64: restrict effects of ARMV7_COMPAT_CPUINFO to ARMv7 tasks

Since ARMV7_COMPAT_CPUINFO only exists to support existing ARMv7
binaries, restrict its effects to compat tasks

Bug: 16819658

Change-Id: I1092de596c7822d23f5f3f8a05b417a3cb49f593
Signed-off-by: Greg Hackmann <ghackmann@google.com>