Add shader for Clamp_SI8_opaque_D32_filter_DX.

Adds a NEON optimized shader for SI8_opaque_D32_filter_DX when
running with clamped tile mode.
Improves performance of browser.

Change-Id: I0e1fa03d4104210953b7ec81ce10eba5f77459cc
Signed-off-by: Henrik Smiding <henrik.smiding@stericsson.com>
Signed-off-by: Patrik Ryd <patrik.ryd@stericsson.com>