If a legacy BIOS has enabled PS/2 mouse input, the bytes received on
port 0x60 may come from either the keyboard or the mouse. Currently
we treat all bytes as keyboard input, which means mouse input will be
translated into arbitrary key codes. This may cause a memory test to
be interrupted or aborted. We should instead disable or ignore any
mouse input.
Although it should be possible to reconfigure the PS/2 controller to
disable mouse input, it's quite likely that there's some quirky H/W
out there that makes this more complicated than it seems. The simple
solution is to detect mouse input by checking whether bit 5 of the
received byte is set and discarding it if so.
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