In testing environment, to avoid accidentally enabling flash
encryption on a device, CONFIG_SECURE_FLASH_REQUIRE_ALREADY_ENABLED
can be set. If set, the bootloader will refuse to boot if flash
encryption is not enabled, instead of enabling it.
This MR improves existing flash encryption document to provide simplified steps
Adds two new modes for user: Development & Release
Adds a simple example
Supports encrypted write through make command
Using xxx_periph.h in whole IDF instead of xxx_reg.h, xxx_struct.h, xxx_channel.h ... .
Cleaned up header files from unnecessary headers (releated to soc/... headers).