The 'ot' variables (operand type?) hold the log2(byte size) of
the operand being manipulated.  This is the same as the MO_SIZE
subset of the TCGMemOp.  Indeed, we often pass 'ot' to the
tcg_gen_qemu_ld/st functions.

Changing the type from 'int' makes it easier to see what domain
the variable should be.

This does require adding some default cases to some switch statements,
to avoid the 'unhandled enumeration value' warning that would result
from the change of type.
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NRichard Henderson <rth@twiddle.net>