altos: Do not release interrupts from any pollchar function

altos: Do not release interrupts from any pollchar function

getchar relies on interrupts being blocked across the pollchar calls
and into the sleep call or it may go to sleep with data pending.

This prefixes all pollchar functions with _ to indicate that they are
to be called with interrupts blocked and eliminates all interrupt
manipulation calls from within the pollchar functions.

Signed-off-by: Keith Packard <keithp@keithp.com>