configs: ti: use standard configuration nodes naming

configs: ti: use standard configuration nodes naming

Currently, any u-boot bootloader for ti armv7 platforms using
DEFAULT_FIT_TI_ARGS to boot with a fitimage (boot_fit = 1)
doesn't boot when built with Yocto Poky (openembedded-core).

  ## Loading kernel from FIT Image at 90000000 ...
  Could not find configuration node
  ERROR: can't get kernel image!

Arago forked the kernel-fitimage class [1] and altered the
configuration nodes naming while adding the OPTEE support by
using FITIMAGE_CONF_BY_NAME by default [2].

The "upstream" kernel-fitimage class from openembedded-core still
add the "conf-" prefix for each configuration nodes [3].

The ITS file format (from doc/uImage.FIT/source_file_format.txt)
is not really accurate with the expected naming of these nodes.
But in practice the "conf-" prefix is widely used.

When the FIT image support has been added for ti armv7 platforms
the naming from Arago has been used [3]. Fix this issue by adding
the prefix expected by the ITS file generated by kernel-fitimage
class from openembedded-core.

[1] http://arago-project.org/git/meta-arago.git?p=meta-arago.git;a=commitdiff;h=719ab1b2098bcdc59c249e3529fa82cb1b9130e6
[2] http://arago-project.org/git/meta-arago.git?p=meta-arago.git;a=commitdiff;h=f23f2876a0cda89241d031bb7ba0b4256ed90035
[3] https://git.openembedded.org/openembedded-core/tree/meta/classes/kernel-fitimage.bbclass?h=yocto-3.1.13#n290
[3] 1e93cc8473e4fe018aececc8ed3bf8fc2b3ff561

Signed-off-by: Romain Naour <romain.naour@smile.fr>
Cc: Tom Rini <trini@konsulko.com>
Reviewed-by: Denys Dmytriyenko <denys@konsulko.com>