Pattern/GL: Avoid texture creation for radial gradients

Pattern/GL: Avoid texture creation for radial gradients
with 2 color stops

When there are only two color stops in the gradient, we can avoid
creating textures before hand, and directly calculate the gradient color
in the fragment shader. This speeds up gradient pattern rendering.

Change-Id: I758b7bc8f37293edbe546fcc4a55f71a7f3c55ae
Signed-off-by: nisanthmp <nisanth.mp@samsung.com>