[U-Boot] Silencing SPL output

[Chris Packham]

This is probably something of a foot-gun but here we go...

I was wondering if it's worth providing the ability to silence the
output from the SPL. CONFIG_SILENT_CONSOLE exist for u-boot proper but
the SPL preloader_console_init bypasses anything that would set
GD_FLG_SILENT. Even if it didn't the SPL probably doesn't have access
to any environment that would allow it to be set/unset.

I was thinking about adding a SPL specific CONFIG option that would
set GD_FLG_SILENT (probably in spl_init). Aside from re-compiling
there wouldn't be any way of making the SPL loud. Is this a reasonable
idea or is it just asking for boards to be bricked with no way of
telling what went wrong?

Thanks,
Chris