i965: Use float calculations when double is unnecessary.

i965: Use float calculations when double is unnecessary.

Literals without an f/F suffix are of type double, and implicit
conversion rules specify that the float in (float op double) be
converted to a double before the operation is performed. I believe float
execution was intended (in nearly all cases) or is sufficient (in the
case of gen7_urb.c).

Removes a lot of float <-> double conversion instructions and replaces
many double instructions with float instructions which are cheaper.

   text     data      bss      dec      hex  filename
4928659   195160    26192  5150011   4e953b  i965_dri.so before
4928315   195152    26192  5149659   4e93db  i965_dri.so after

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