x86/pci: Remove #ifdef __KERNEL__ guard from <asm/pci.h>

pci.h is not a UAPI header, so the __KERNEL__ ifdef is rather pointless.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20191113071836.21041-4-hch@lst.de