arm/sbsa-ref: move to Neoverse-N2 as default

arm/sbsa-ref: move to Neoverse-N2 as default

Moving to Neoverse-N2 gives us several cpu features to use for expanding
our platform:

- branch target identification
- pointer authentication
- RME for confidential computing
- RNG for EFI_PROTOCOL_RNG
- SVE being enabled by default

We do not go for "max" as default to have stable set of features enabled
by default. It is still supported and can be selected with "--cpu"
argument.

Signed-off-by: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>
Reviewed-by: Leif Lindholm <quic_llindhol@quicinc.com>
Message-id: 20240523165353.6547-1-marcin.juszkiewicz@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>