esp8266

The following two functions in bootloader_support are private now:
* esp_secure_boot_verify_sbv2_signature_block()
* esp_secure_boot_verify_rsa_signature_block()
They have been moved into private header files
inside bootloader_private/

* Removed bootloader_reset_reason.h and
  bootloader_common_get_reset_reason() completely.
  Alternative in ROM component is available.

* made esp_efuse.h independent of target-specific rom header