<https://webkit.org/b/119912> Fix WebKit build error when SVG is disabled(broken...

<https://webkit.org/b/119912> Fix WebKit build error when SVG is disabled(broken since r154174)

Patch by Arunprasad Rajkumar <arurajku@cisco.com> on 2013-08-16
Reviewed by Simon Fraser.

No new tests required, just a build fix.

Since r154174 CSS keywords alpha and luminance used by -webkit-mask-source-type. Move those
keywords from SVGCSSValueKeywords.in to CSSValueKeywords.in.

* css/CSSValueKeywords.in:
* css/SVGCSSValueKeywords.in:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@154203 268f45cc-cd09-0410-ab3c-d52691b4dbfc