Delete platform folder?

Hi,

I'm doing some cleanup work on the Makefiles in incubator-nuttx. See https://github.com/apache/incubator-nuttx/issues/5205 for more details.

I'm trying to figure out exactly what the `platform` folder is being used for.

It currently only has one non-dummy entry: `platform/mikroe-stm32f4`.

Q1: Is this leftover from the nuttx-app split?
Q2: Should `platform/mikroe-stm32f4` be moved to another location?
`platform/mikroe-stm32f4/mikroe_configdata.c` implements `platform_setconfig` and `platform_getconfig`. The other functions that implement that API are defined in `graphics/nxwm/src/ccalibration.cxx`, `graphics/nxwm/src/nxwm_main.cxx`, `graphics/twm4nx/apps/ccalibration.cxx`. Maybe the correcct location is under `graphics`.

Also, it looks like most of the implementation of `platform/mikroe-stm32f4/mikroe_configdata.c` are guarded by `CONFIG_MIKROE_STM32F4_CONFIGDATA_FS` and `CONFIG_MIKROE_STM32F4_CONFIGDATA_PART`. I couldn't find any defconfig where those were set to `y`.

Q3: Is we move/delete `mikroe-stm32f4`, should we also delete the `platform` folder? At first look it doesn't make sense for apps to have a platform specific code.