i965: Change the type of booleans to D.

i965: Change the type of booleans to D.

This is a revert of commit 4656c14e ("i965/fs: Change the type of
booleans to UD and emit correct immediates") plus some small additional
fixes, like casting ctx->Const.UniformBooleanTrue to int and changing UD
to D in the ir_unop_b2f cases. Note that it's safe to leave 0x3f800000
as UD and as a literal it's more recognizable than 1065353216.

Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>