qemu-x86*_defconfig: Enable CONFIG_PCI_INIT_R

Enable CONFIG_PCI_INIT_R for qemux86 and qemux86-64 pci enumeration during
boot in order to eliminate the custom preboot commands in
include/configs/qemu-x86.h.

Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>