fpga/system_build.tcl: Tweak implementation optimization settings
fpga/system_build.tcl: Tweak implementation optimization settings

This is what ADI HDL uses. I trust that they know what they're doing.

Signed-off-by: Ola Jeppsson <793f970c52ded1276b9264c742f19d1888cbaf73@adapteva.com>

olajep/oh,parallella/oh,parallella/oh,olajep/oh,olajep/oh,parallella/oh,parallella/oh,olajep/oh