x86/platform/uv: Make SGI UV dependent on CONFIG_PCI

Recent PCI changes stopped exporting PCI constants if !CONFIG_PCI,
which made the UV build fail:

  arch/x86/kernel/apic/x2apic_uv_x.c:843:16: error: ‘PCI_VGA_STATE_CHANGE_BRIDGE’ undeclared (first use in this function)
  arch/x86/kernel/apic/x2apic_uv_x.c:1023:2: error: implicit declaration of function ‘pci_register_set_vga_state’ [-Werror=implicit-function-declaration]

As it's unlikely that an UV bootup will get far without PCI
enumeration, make the platform Kconfig switch (CONFIG_X86_UV)
depend on CONFIG_PCI=y.

Cc: Robin Holt <holt@sgi.com>
Cc: Dimitri Sivanich <sivanich@sgi.com>
Cc: Russ Anderson <rja@sgi.com>
Cc: Mike Travis <travis@sgi.com>
Cc: Jack Steiner <steiner@sgi.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>