common/console.c: Fix unused warning with console_doenv()

Newer versions of LLVM-7 will provide an unused function warning over
console_doenv() in the case of SYS_CONSOLE_IS_IN_ENV not being enabled
as can be the case in SPL.  Add guards around this function.

Signed-off-by: Tom Rini <trini@konsulko.com>
1 file changed