st/mesa: relax EXT_shader_image_load_store enable

st/mesa: relax EXT_shader_image_load_store enable

There's no reason to bring format-less load requirement into this
extension. It requires a size to be provided, and a compatible format is
computed from the size + data type. For example

  layout(size1x32) uniform iimage1D image;

becomes

  DCL IMAGE[0], 1D, PIPE_FORMAT_R32_SINT, WR

whereas PIPE_CAP_IMAGE_LOAD_FORMATTED is designed to allow
PIPE_FORMAT_NONE to be provided as a format and still enable LOAD
operations to be performed.

So the shader has all the information it needs about the format.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>