NuttX build in place

- cmake NuttX build wrapper compile in place instead of copying source tree to build directory
    - slightly faster skipping necessary copying (depending on system)
    - allows debugging in place
    - easier to work directly in NuttX following official documentation
    - simplifies overall build which should make it easier to resolve any remaining NuttX dependency issues in the build system
 - the downside is switching back and forth between different builds always require rebuilding NuttX, but I think this is worth the improved developer experience
 - also no longer builds px4io and bootloader in every single build, for most users these rarely change and we're wasting a lot of build time

Kconfig

@@ -63,13 +63,10 @@ menu "Toolchain"
         help
             relative path to the ROMFS root directory
 
-    config BOARD_BUILD_BOOTLOADER
-        bool "Enable bootloader"
-        help
-            flag to enable building and including the bootloader config
-
     config BOARD_IO
         string "IO board name"
+        default "px4_io-v2_default"
+        depends on DRIVERS_PX4IO
         help
             name of IO board to be built and included in the ROMFS (requires a valid ROMFSROOT)