emul: mspi: Add the mspi controller emulator

Add bus emulator support for MSPI and the MSPI controller emulator.
The mspi_emul.c not only serves as an emulator but also provides an
example implementation of the MSPI API. It does not actually do anything
other than validating parameters and forwarding transceive request back
to the device driver emulators.

Signed-off-by: Swift Tian <swift.tian@ambiq.com>

Author: swift-tk

drivers/mspi/CMakeLists.txt

@@ -3,3 +3,4 @@
 zephyr_syscall_header(${ZEPHYR_BASE}/include/zephyr/drivers/mspi.h)
 
 zephyr_library()
+zephyr_library_sources_ifdef(CONFIG_MSPI_EMUL        mspi_emul.c)

drivers/mspi/Kconfig

@@ -59,4 +59,6 @@ module = MSPI
 module-str = mspi
 source "subsys/logging/Kconfig.template.log_config"
 
+source "drivers/mspi/Kconfig.mspi_emul"
+
 endif # MSPI

drivers/mspi/Kconfig.mspi_emul

@@ -0,0 +1,17 @@
+# Copyright (c) 2024, Ambiq Micro Inc. <www.ambiq.com>
+# SPDX-License-Identifier: Apache-2.0
+
+config MSPI_EMUL
+	bool "MSPI emulator"
+	default y
+	depends on DT_HAS_ZEPHYR_MSPI_EMUL_CONTROLLER_ENABLED
+	depends on EMUL
+	select MSPI_XIP
+	select MSPI_SCRAMBLE
+	select MSPI_TIMING
+	select GPIO
+	help
+	  Enable the MSPI emulator driver. This is a fake driver in that it
+	  does not talk to real hardware. Instead it talks to emulation
+	  drivers that pretend to be devices on the emulated MSPI bus. It is
+	  used for testing drivers for MSPI devices.