target/arm: Allow board models to specify initial NS VTOR

target/arm: Allow board models to specify initial NS VTOR

Currently we allow board models to specify the initial value of the
Secure VTOR register, using an init-svtor property on the TYPE_ARMV7M
object which is plumbed through to the CPU.  Allow board models to
also specify the initial value of the Non-secure VTOR via a similar
init-nsvtor property.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210520152840.24453-10-peter.maydell@linaro.org