image: Shorten FIT_ENABLE_SHAxxx_SUPPORT

The ENABLE part of this name is redundant, since all boolean Kconfig
options serve to enable something. The SUPPORT part is also redundant
since Kconfigs can be assumed to enable support for something. Together
they just serve to make these options overly long and inconsistent
with other options.

Rename FIT_ENABLE_SHAxxx_SUPPORT to FIT_SHAxxx

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>