monitor: Use TARGET_PRI*PHYS to avoid TARGET_PHYS_ADDR_BITS ifdef

Now we have TARGET_PRI*PHYS for printing target_phys_addr_t values,
we can use them in monitor.c rather than having duplicate code
in two arms of a TARGET_PHYS_ADDR_BITS ifdef.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>