Update version for v2.1.0-rc4 release

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
hw/arm/virt: fix pl031 addr typo

pl031's base address should be 0x9010000, not 0x90010000, otherwise
it sits in ram when configuring a guest with greater than 1G.

Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Update version for v2.1.0-rc5 release

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>