mv88e6xxx: Cache scratch config3 of 6352

mv88e6xxx: Cache scratch config3 of 6352

Changes:

1. Add g2_scratch_config3 member to mv88e6xxx_chip.

2. Add mv88e6352_g2_cache_global_scratch_config3  which reads the
CONFIG3 value from the scratch register and caches it.

3. Call this function in mv88e6352_reset.

Co-developed-by: Thomas Eckerman <thomas.eckerman.ext@ericsson.com>
Signed-off-by: Thomas Eckerman <thomas.eckerman.ext@ericsson.com>
Signed-off-by: Fidan Aliyeva <fidan.aliyeva.ext@ericsson.com>
Link: https://patch.msgid.link/20260521202924.727929-3-fidan.aliyeva.ext@ericsson.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>