It's not practical to detect tools within the toolchain environment
for various reasons, so just assume the tools are there if the user
says they are.
Before this commit, the tools would be searched outside the toolchain
environment, which of course would always fail for Vivado, ISE, etc.
On Xilinx devices, flip-flops are reset to their initial state with
an internal global reset network, but this network is deasserted
asynchronously to user clocks. Use BUFGCE and STARTUP to hold default
clock low until after GWE is deasserted.
Previously changed in 27063a3b.
I haven't realized the .bin file is the same as the .bit file without
a small header. That means generating it is free and it's just easier
to let programming tools to be able to always rely on its existence.
