1. separate rom include files and linkscript to esp_rom
2. modefiy "include rom/xxx.h" to "include esp32/rom/xxx.h"
3. Forward compatible
4. update mqtt
Makes spiffs component runnable on host. Depends on the host library build
of flash emulator. Includes a basic sanity test of
mounting a volume, opening a file, writing to the file, reading the file,
closing the file and unmounting volume.
Makes the entirety of the wl API runnable on host. Flash emulator
is separated into spi_flash component directory to be reused by
other storage components.
