nvme: Split out PCI support

Apple SoCs have an integrated NVMe controller that isn't connected
over a PCIe bus. In preparation for adding support for this NVMe
controller, split out the PCI support into its own file. This file
is selected through a new CONFIG_NVME_PCI Kconfig option, so do
a wholesale replacement of CONFIG_NVME with CONFIG_NVME_PCI.

Signed-off-by: Mark Kettenis <kettenis@openbsd.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested on: Macbook Air M1
Tested-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/develop/driver-model/nvme.rst b/doc/develop/driver-model/nvme.rst
index 736c0a0..fd0c0f0 100644
--- a/doc/develop/driver-model/nvme.rst
+++ b/doc/develop/driver-model/nvme.rst
@@ -40,6 +40,7 @@
 Config options
 --------------
 CONFIG_NVME	Enable NVMe device support
+CONFIG_NVME_PCI	Enable PCIe NVMe device support
 CONFIG_CMD_NVME	Enable basic NVMe commands
 
 Usage in U-Boot