i965: Add devinfo->gen assertions for acc_wr_control.
i965: Add devinfo->gen assertions for acc_wr_control.

... and for flag_subreg_nr since it's right near by.

Reviewed-by: Iago Toral Quiroga <a847aabaac44184372f6b1cd1a59aa254daaeb0b@igalia.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler