With printch() the console messages are sent out one character at a time
which is agonizingly slow especially with semihosting as the whole trap
intercept, remote byte access, and system resume danse is performed for
every single character across a relatively slow remote debug connection.

Let's use printascii() to send a whole string at once. This is also going
to be more efficient, albeit to a quite lesser extent, with serial ports
as well.
Signed-off-by: NNicolas Pitre <nico@linaro.org>
Signed-off-by: NRussell King <rmk+kernel@armlinux.org.uk>