iris: Enable ARB_gl_spirv and ARB_spirv_extensions

This will also "unlock" OpenGL 4.6 for Iris!

v2: Also enable PIPE_CAP_GL_SPIRV_VARIABLE_POINTERS.

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com> [v1]

src/gallium/drivers/iris/iris_screen.c

@@ -200,6 +200,8 @@ iris_get_param(struct pipe_screen *pscreen, enum pipe_cap param)
    case PIPE_CAP_CS_DERIVED_SYSTEM_VALUES_SUPPORTED:
    case PIPE_CAP_TEXTURE_SHADOW_LOD:
    case PIPE_CAP_SHADER_SAMPLES_IDENTICAL:
+   case PIPE_CAP_GL_SPIRV:
+   case PIPE_CAP_GL_SPIRV_VARIABLE_POINTERS:
       return true;
    case PIPE_CAP_FBFETCH:
       return BRW_MAX_DRAW_BUFFERS;