Tegra: include: drivers: introduce spe.h

This patch introduces a header file for the spe-console driver. This
file currently provides a device struct and a registration function
call for clients.

Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>
Change-Id: Ic65c056f5bd60871d8a3f44f2c1210035f878799