php: create recipe for 5.6.12

The difference between 5.6.x and 5.5.x is in http://php.net/migration56


Most improvements in PHP 5.6.x have no impact on existing code.
There are a few incompatibilities and new features that should be
considered, and code should be tested before switching PHP versions
in production environments.

Signed-off-by: Roy Li <rongqing.li@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>