fsi/fsi-master-gpio: Add "no-gpio-delays" option

This adds support for an optional device-tree property that
makes the driver skip all the delays around clocking the
GPIOs and set it in the device-tree of common POWER9 based
OpenPower platforms.

This useful on chips like the AST2500 where the GPIO block is
running at a fairly low clock frequency (25Mhz typically). In
this case, the delays are unnecessary and due to the low
precision of the timers, actually quite harmful in terms of
performance.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reviewed-by: Christopher Bostic <cbostic@linux.vnet.ibm.com>
Tested-by: Joel Stanley <joel@jms.id.au>

arch/arm/boot/dts/aspeed-bmc-opp-romulus.dts

@@ -52,6 +52,7 @@
 		compatible = "fsi-master-gpio", "fsi-master";
 		#address-cells = <2>;
 		#size-cells = <0>;
+		no-gpio-delays;
 
 		clock-gpios = <&gpio ASPEED_GPIO(AA, 0) GPIO_ACTIVE_HIGH>;
 		data-gpios = <&gpio ASPEED_GPIO(AA, 2) GPIO_ACTIVE_HIGH>;