i965/fs: Add fs_reg::is_zero() and is_one(); use for opt_algebraic().

i965/fs: Add fs_reg::is_zero() and is_one(); use for opt_algebraic().

These helper macros save you from writing nasty expressions like:

   if ((inst->src[1].type == BRW_REGISTER_TYPE_F &&
         inst->src[1].imm.f == 1.0) ||
        ((inst->src[1].type == BRW_REGISTER_TYPE_D ||
          inst->src[1].type == BRW_REGISTER_TYPE_UD) &&
         inst->src[1].imm.u == 1)) {

Instead, you simply get to write inst->src[1].is_one().  Simple.
Also, this makes the FS backend match the VS backend (which has these).

This patch also converts opt_algebraic to use the new helper functions.
As a consequence, it will now also optimize integer-typed expressions.

Reviewed-by: Eric Anholt <eric@anholt.net>