arm/cpu: Add sysreg definitions in cpu-sysregs.h

arm/cpu: Add sysreg definitions in cpu-sysregs.h

This new header contains macros that define aarch64 registers.
In a subsequent patch, this will be replaced by a more exhaustive
version that will be generated from linux arch/arm64/tools/sysreg
file. Those macros are sufficient to migrate the storage of those
ID regs from named fields in isar struct to an array cell.

[CH: reworked to use different structures]
[CH: moved accessors from the patches first using them to here,
     dropped interaction with writable registers, which will happen
     later]
[CH: use DEF magic suggested by rth]
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Sebastian Ott <sebott@redhat.com>
Signed-off-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
Message-id: 20250617153931.1330449-2-cohuck@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>