kernel: Move to Linux 4.16.1-openpower2

Move to the 4.16 series. Changes to patches:

 - "tg3: APE heartbeat changes" patch was merged upstream and can be
 dropped

 - "powerpc/mm/radix: Fix checkstops caused by invalid tlbiel" was found
 when testing with 4.16.1-openpower1 and has been posted upstream

A few new options are turned off by default as they are not useful to
petitboot. In the future we may enable DEFERRED_STRUCT_PAGE_INIT, but it
defaults to off for now.

We bump the buildroot repository in order to support the new kernel
version.

Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/openpower/linux/0001-xhci-Reset-controller-on-xhci-shutdown.patch b/openpower/linux/0001-xhci-Reset-controller-on-xhci-shutdown.patch
index 3675f53..55c0f56 100644
--- a/openpower/linux/0001-xhci-Reset-controller-on-xhci-shutdown.patch
+++ b/openpower/linux/0001-xhci-Reset-controller-on-xhci-shutdown.patch
@@ -14,10 +14,10 @@
  1 file changed, 1 insertion(+)
 
 diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
-index a7c99e121cc6..f953c94b2c5e 100644
+index 5d37700ae4b0..27848c3226a4 100644
 --- a/drivers/usb/host/xhci.c
 +++ b/drivers/usb/host/xhci.c
-@@ -722,6 +722,7 @@ static void xhci_shutdown(struct usb_hcd *hcd)
+@@ -717,6 +717,7 @@ static void xhci_shutdown(struct usb_hcd *hcd)
  	/* Yet another workaround for spurious wakeups at shutdown with HSW */
  	if (xhci->quirks & XHCI_SPURIOUS_WAKEUP)
  		pci_set_power_state(to_pci_dev(hcd->self.sysdev), PCI_D3hot);