dt-bindings: PCI: intel: Fix dt_binding_check compilation failure

Remove <dt-bindings/clock/intel,lgm-clk.h> dependency as
it is not present in the mainline tree. Use numeric value
instead of LGM_GCLK_PCIE10 macro.

Signed-off-by: Dilip Kota <eswara.kota@linux.intel.com>
[robh: Also drop interrupt-parent from example]
Signed-off-by: Rob Herring <robh@kernel.org>