soc/intel/skylake: Add 4 missing root ports to chipset dt

The Kaby Lake PCH can have up to 24 PCIe root ports. Thus, add 4 missing
root ports to the chipset devicetree.

Change-Id: I443fb736873d47f1b6fe7718a10e1bb4ae5df2a6
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/48947
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-by: Michael Niewöhner <foss@mniewoehner.de>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/intel/skylake/chipset.cb

@@ -31,6 +31,10 @@ chip soc/intel/skylake
 		device pci 1b.1 alias pcie_rp18    off end # PCI Express Port 18
 		device pci 1b.2 alias pcie_rp19    off end # PCI Express Port 19
 		device pci 1b.3 alias pcie_rp20    off end # PCI Express Port 20
+		device pci 1b.4 alias pcie_rp21    off end # PCI Express Port 21
+		device pci 1b.5 alias pcie_rp22    off end # PCI Express Port 22
+		device pci 1b.6 alias pcie_rp23    off end # PCI Express Port 23
+		device pci 1b.7 alias pcie_rp24    off end # PCI Express Port 24
 		device pci 1c.0 alias pcie_rp1     off end # PCI Express Port 1
 		device pci 1c.1 alias pcie_rp2     off end # PCI Express Port 2
 		device pci 1c.2 alias pcie_rp3     off end # PCI Express Port 3