Add Linux SPI device SWD adapter support

To alleviate the need to bitbang SWD, I've written a SWD SPI
implementation. This code is inspired by the work of luppy@appkaki.com
as shown at github.com/lupyuen/openocd-spi but with the desire to be
more generic. This implementation makes use of the more common 4 wire
SPI port using full duplex transfers to be able to capture the SWD ACK
bits when a SWD TX operation is in progress.

TEST:
  Connects successfully with the following combinations:
  Hosts:
    Raspberry Pi 4B
    Unnamed Qualcomm SoC with QUPv3 based SPI port
  Targets:
    Raspberry Pi 2040
    Nordic nRF52840
    NXP RT500

Change-Id: Ic2f38a1806085d527e6f999a3d15aea6f32d1019
Signed-off-by: Richard Pasek <rpasek@google.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/8645
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-by: zapb <dev@zapb.de>
Tested-by: jenkins

src/jtag/interfaces.c

@@ -123,6 +123,9 @@ struct adapter_driver *adapter_drivers[] = {
 #if BUILD_LINUXGPIOD == 1
 		&linuxgpiod_adapter_driver,
 #endif
+#if BUILD_LINUXSPIDEV == 1
+		&linuxspidev_adapter_driver,
+#endif
 #if BUILD_XLNX_PCIE_XVC == 1
 		&xlnx_pcie_xvc_adapter_driver,
 #endif