SVA to check clock toggling for a fixed number of cycles

In reply to ben@SystemVerilog.us:

sclk must be stable and toggling before ACK asserts (min 4 SCLKs)
 sclk must be stable and toggling after ACK de-asserts (min 8 SCLKs)
 sclk must be stable and toggling when both the REQ and ACK are asserted

Here you go, this is what I need to do.

Thanks