FATFS fixes and tests
This MR includes a set of fixes related to FATFS, SDMMC, and wear levelling:
- `esp_vfs_fat_spiflash_mount` uses `FM_SFD` flag when creating the partition. The volume layout (given in `VolToPart` variable) was not compatible with SFD mode, so mkfs was failing. This fixes the volume layout to use "autodetect" for both volumes. Merges https://github.com/espressif/esp-idf/pull/559.
- fix `prepend_drive_to_path`function, which didn't prepend drive to path (while consuming 2k of stack space)
- fix stack overflow in vfs_fat_link function which allocated two 4kbyte `FIL` structures on the stack
- fix support for having two FATFS instances (in flash and SD) mounted at the same time
- unit tests written for FATFS on SDMMC are made common between SDMMC and WL implementations; FATFS unit tests on WL will run during CI
- fix inconsistent definition of PATH_MAX and ARG_MAX (TW12207, TW12104, https://github.com/espressif/esp-idf/issues/289)
See merge request !732