Hello Aditya Nagal,
(1) The Boot ROM code of the i.MX6 is fixed and no source code is provided for it. The features of the Boot ROM code and more detailed information on the boot process can be found on Chapter 8 of the i.MX6Q Reference Manual. The ROM code loads the bootloader (u-boot) can also allow the downloading of programs to be run on the device.
U-boot source code is available.
(2) You may enable interfaces from u-boot itself. (The ROM Code interface functionalities are fixed and limited to the ones specified on the Reference Manual). You may also run them bareboard. There is a SDK which is no longer supported but can be provided as reference by opening a Case.
I hope this information helps!
Regards,