Disable SRL16 until VPR/xc7 supports it.
Disable SRL16 until VPR/xc7 supports it.

Signed-off-by: Keith Rothman <1bc19627a439baf17510dc2d0b2d250c96d445a5@users.noreply.github.com>

SymbiFlow/yosys,SymbiFlow/yosys,SymbiFlow/yosys,SymbiFlow/yosys,SymbiFlow/yosys,SymbiFlow/yosys,SymbiFlow/yosys,SymbiFlow/yosys