Updates the following with changes from verification branches:
* esp_rom linker files
* rtc_cntl and system reg and struct headers
Also updates:
* GDMA driver with new register layout
* esptool submodule commit
Removed the old dynamically allocated GDMA channel approach.
It proved too unreliable as we couldn't not ensure consumers of the mbedtls
would properly free the channels after use.
Replaced by a single shared GDMA channel for AES and SHA, which won't be
released unless user specifically calls API for releasing it.
