target/ppc: Add two missing register callbacks on POWER10

target/ppc: Add two missing register callbacks on POWER10

This patch adds tcg accessors for 2 SPRs which were missing on P10:

- the TBU40 register is used to write the upper 40 bits of the
timebase register. It is used by kvm to update the timebase when
entering/exiting the guest on P9 and above. The missing definition was
causing erratic decrementer interrupts in a pseries/kvm guest running
in a powernv10/tcg host, typically resulting in hangs.

- the missing DPDES SPR was found through code inspection. It exists
unchanged on P10.

Both existed on previous versions of the processor and a bit of git
archaeology hints that they were added while the P10 model was already
being worked on so they may have simply fallen through the cracks.

Signed-off-by: Frederic Barrat <fbarrat@linux.ibm.com>
Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
Message-Id: <20220411125900.352028-1-fbarrat@linux.ibm.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>