target/ppc: cpu_init: Deduplicate 745/755 SPR registration

target/ppc: cpu_init: Deduplicate 745/755 SPR registration

The 745 and 755 can share the HID registration, so move it all into
register_755_sprs, which applies for both CPUs.

Also rename that function to register_745_sprs, since the 745 is the
earliest of the two. This will help with separating 755-specific
registers in a subsequent patch.

Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Message-Id: <20220216162426.1885923-14-farosas@linux.ibm.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>