target/ppc: removed VSCR from SPR registration

target/ppc: removed VSCR from SPR registration

Since vscr is not an spr, its initialization was removed from the
spr registration functions, and moved to the relevant init_procs.

We may look into adding vscr to the reset path instead of the init
path (as suggested by David Gibson), but this looked like a good
enough solution for now.

Signed-off-by: Bruno Larsen (billionai) <[email protected]>
Message-Id: <20210430193533[email protected]>
Reviewed-by: Richard Henderson <[email protected]>
Signed-off-by: David Gibson <[email protected]>