Enable Cortex-A53-specific code paths by default if core is detected.

Enable Cortex-A53-specific code paths by default if core is detected.
https://bugs.webkit.org/show_bug.cgi?id=138499

Patch by Akos Kiss <akiss@inf.u-szeged.hu> on 2014-11-10
Reviewed by Csaba Osztrogonác.

On ARM64/Linux, check /proc/cpuinfo for CPU part 0xd03 (signaling
Cortex-A53) and set the initial value of WTF_CPU_ARM64_CORTEXA53 to true
if found.

Since on ARM64/Linux the part number that cpuinfo reports depends on
the core the query is run on, the check is bound to and executed on the
available cores one by one.

* Source/cmake/OptionsCommon.cmake:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@175804 268f45cc-cd09-0410-ab3c-d52691b4dbfc