powerpc: Replace CONFIG_4xx with CONFIG_44x

Replace 4xx usage with 44x, and replace 4xx_SOC with 44x.

Also, as pointed out by Christophe, if 44x || BOOKE can be simplified to
just test BOOKE, because 44x always selects BOOKE.

Retain the CONFIG_4xx symbol, as there are drivers that use it to mean
4xx || 44x, those will need updating before CONFIG_4xx can be removed.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240628121201.130802-6-mpe@ellerman.id.au