ppc/pnv: Add new PowerPC Special Purpose Registers (RWMR)

ppc/pnv: Add new PowerPC Special Purpose Registers (RWMR)

Register RWMR - Region Weighted Mode Register
for privileged access in Power9 and Power10

It controls what the SPURR register produces.

Specs:
 - Power10: https://files.openpower.foundation/s/EgCy7C43p2NSRfR

TCG does not model SMT priority, timing, resource controls
and status so this register has no effect for now.

[npiggin: adjust changelog]
Signed-off-by: dan tan <dantan@linux.ibm.com>
Message-ID: <20250116154226.13376-1-dantan@linux.vnet.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>