php: add PHP_VERSION_MAJOR variable

Add PHP_VERSION_MAJOR variable to php.mk for use by other packages.
E.g. to install the Ioncube loader binary, it is necessary to
know the PHP major version.

Signed-off-by: Floris Bos <bos@je-eigen-domein.nl>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/php/php.mk

@@ -4,7 +4,8 @@
 #
 ################################################################################
 
-PHP_VERSION = 5.6.8
+PHP_VERSION_MAJOR = 5.6
+PHP_VERSION = $(PHP_VERSION_MAJOR).8
 PHP_SITE = http://www.php.net/distributions
 PHP_SOURCE = php-$(PHP_VERSION).tar.xz
 PHP_INSTALL_STAGING = YES