aspeed: Add P-Bus clock in ast2500 clock driver

Add P-Bus Clock support to ast2500 clock driver.
This is the clock used by I2C devices.

Signed-off-by: Maxim Sloyko <maxims@google.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/clk/aspeed/clk_ast2500.c b/drivers/clk/aspeed/clk_ast2500.c
index 5047312..9e4c66e 100644
--- a/drivers/clk/aspeed/clk_ast2500.c
+++ b/drivers/clk/aspeed/clk_ast2500.c
@@ -110,6 +110,17 @@
 		rate = ast2500_get_mpll_rate(clkin,
 					     readl(&priv->scu->m_pll_param));
 		break;
+	case BCLK_PCLK:
+		{
+			ulong apb_div = 4 + 4 * ((readl(&priv->scu->clk_sel1)
+						  >> SCU_PCLK_DIV_SHIFT) &
+						 SCU_PCLK_DIV_MASK);
+			rate = ast2500_get_hpll_rate(clkin,
+						     readl(&priv->scu->
+							   h_pll_param));
+			rate = rate / apb_div;
+		}
+		break;
 	case PCLK_UART1:
 		rate = ast2500_get_uart_clk_rate(priv->scu, 1);
 		break;