nimble/phy: Add README for Dialog CMAC PHY

nimble/drivers/dialog_cmac/README.md

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+
+## How to run NimBLE controller on Dialog DA1469x
+
+Dialog DA1469x has separate Cortex-M0+ core inside CMAC hw block which can run
+NimBLE controller. This means DA1469x can run full NimBLE stack: host is running
+on M33 core while controller is running on M0+ core. Both communicate using
+standard HCI H4 protocol exchanged over mailboxes located in shared memory.
+
+### Basic setup
+
+In order to run full NimBLE stack on DA1469x you will need two newt targets: one
+for M33 (e.g. `dialog_da1469x-dk-pro` BSP) and one for M0+ (`dialog_cmac` BSP).
+
+Once everything is configured properly, you only need to build target for M33.
+Target configured for M0+ will be build automatically and image is linked with
+M33 image so everything can be flashed at once just as if there is only single
+target used.
+
+Target for M33 should be set and configured as any other BLE application. In
+order to use NimBLE controller on CMAC, set proper HCI transport via syscfg:
+
+    BLE_HCI_TRANSPORT: dialog_cmac
+
+This will include proper transport, driver and add M0+ target to build process.
+
+For M0+, there is sample target provided in `targets/dialog_cmac` and it's used
+by default unless overrided by syscfg in M33 target:
+
+    CMAC_IMAGE_TARGET_NAME: "@apache-mynewt-nimble/targets/dialog_cmac"
+
+If you wish to create own target for M0+, make sure your target is set the same
+way (`app`, `bsp` and `build_profile`) as sample. Also it is recommended to use
+syscfg settings from sample target in new target.
+
+### NimBLE configuration
+
+Since host and controller are running on different cores, they both use separate
+configuration: host configuration is in M33 target, controller configuration is
+in M0+ target. There is currently no way to automatically synchronize both, so
+care needs to be taken when enabling features in either of targets.
+
+A possible workaround is to use separate `.yml` file with all the NimBLE syscfg
+values settings and include it in both targets using `$import` directive which
+is supported by recent versions of `newt` tool.
+
+### Advanced settings
+
+(tbd)