tslib: disable raw input plugin under kernel < v3.12

tslib: disable raw input plugin under kernel < v3.12

The SYN_CNT input code was added in kernel v3.12.

Fixes:
http://autobuild.buildroot.net/results/5cd/5cdb9d22092e9222cc7e8fe8dd3936305a5d371d/
http://autobuild.buildroot.net/results/211/2115038caff1e036cbc9dcb5cb6905abe643552a/
http://autobuild.buildroot.net/results/c79/c79de6fdd5cfe406979941790276296b6d1ec0b8/

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>