Input: tegra-kbc - allocate pdata before using it

Following commit broke DT support for tegra-kbc by removing pdata
allocation completely:

   commit 023cea0e
   Author: Shridhar Rasal <srasal@nvidia.com>
   Date:   Fri Feb 3 00:27:30 2012 -0800

       Input: tegra-kbc - allow skipping setting up some of GPIO pins

This patch restores it.

Signed-off-by: Viresh Kumar <viresh.kumar@st.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>