env: ti: boot: Show boot status information

Add tracing printings to Linux/Android boot commands, so that we can see
what's going on. Helps to trace possible bugs on early stages and
improves the output for user (which is especially useful, because we
have a bunch of boot commands executing one by one).

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Reviewed-by: Tom Rini <trini@konsulko.com>