target/arm: Rename cp15.c6_rgnr to pmsav7.rnr

Almost all of the PMSAv7 state is in the pmsav7 substruct of
the ARM CPU state structure. The exception is the region
number register, which is in cp15.c6_rgnr. This exception
is a bit odd for M profile, which otherwise generally does
not store state in the cp15 substruct.

Rename cp15.c6_rgnr to pmsav7.rnr accordingly.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 1501153150-19984-4-git-send-email-peter.maydell@linaro.org