target-arm: Allow STATE_BOTH reginfo descriptions for more than cp14

target-arm: Allow STATE_BOTH reginfo descriptions for more than cp14

Currently the STATE_BOTH shorthand for allowing a single reginfo struct
to define handling for both AArch32 and AArch64 views of a register
only permits this where the AArch32 view is in cp15. It turns out that
the debug registers in cp14 also have neatly lined up encodings;
allow these also to share reginfo structs by permitting a STATE_BOTH
reginfo to specify the .cp field (and continue to default to 15 if
it is not specified).

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>