target/ppc: cpu_init: Decouple G2 SPR registration from 755

target/ppc: cpu_init: Decouple G2 SPR registration from 755

We're considering these two to be in different CPU families (6xx and
7xx), so keep their SPR registration separate.

The code was copied into register_G2_sprs and the common function was
renamed to apply only to the 755.

Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Message-Id: <20220216162426.1885923-9-farosas@linux.ibm.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>