gpio: at91_gpio: remove CPU_HAS_PIO3 macro

The intention of the removal is the preparation to introduce the
new AT91 PIO pinctrl driver.

Use the union to make the PIO3 and PIO2's registers be together
and make their offset aligned.

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/net/at91_emac.c b/drivers/net/at91_emac.c
index be3d82e..eb8d2b3 100644
--- a/drivers/net/at91_emac.c
+++ b/drivers/net/at91_emac.c
@@ -333,7 +333,7 @@
 		ATMEL_PMX_AA_ETXEN |	ATMEL_PMX_AA_EREFCK;
 
 	writel(value, &pio->pioa.pdr);
-	writel(value, &pio->pioa.asr);
+	writel(value, &pio->pioa.mux.pio2.asr);
 
 #ifdef CONFIG_RMII
 	value = ATMEL_PMX_BA_ERXCK;
@@ -344,7 +344,7 @@
 		ATMEL_PMX_BA_ETX3 |	ATMEL_PMX_BA_ETX2;
 #endif
 	writel(value, &pio->piob.pdr);
-	writel(value, &pio->piob.bsr);
+	writel(value, &pio->piob.mux.pio2.bsr);
 
 	at91_periph_clk_enable(ATMEL_ID_EMAC);