x86: pci: Add a function to clear and set PCI config regs

At present the x86 pre-DM equivalent of pci_bus_clrset_config32() does not
exist. Add it to simplify PCI init code on x86.

Also add the missing functions to this header.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/x86/cpu/pci.c b/arch/x86/cpu/pci.c
index c621825..0ccde19 100644
--- a/arch/x86/cpu/pci.c
+++ b/arch/x86/cpu/pci.c
@@ -16,6 +16,10 @@
 #include <asm/io.h>
 #include <asm/pci.h>
 
+/*
+ * TODO(sjg@chromium.org): Drop the first parameter from each of these
+ * functions since it is not used.
+ */
 int pci_x86_read_config(struct udevice *bus, pci_dev_t bdf, uint offset,
 			ulong *valuep, enum pci_size_t size)
 {
@@ -54,6 +58,21 @@
 	return 0;
 }
 
+int pci_x86_clrset_config(struct udevice *bus, pci_dev_t bdf, uint offset,
+			  ulong clr, ulong set, enum pci_size_t size)
+{
+	ulong value;
+	int ret;
+
+	ret = pci_x86_read_config(bus, bdf, offset, &value, size);
+	if (ret)
+		return ret;
+	value &= ~clr;
+	value |= set;
+
+	return pci_x86_write_config(bus, bdf, offset, value, size);
+}
+
 void pci_assign_irqs(int bus, int device, u8 irq[4])
 {
 	pci_dev_t bdf;