powerpc/cputable: Split cpu_specs[] out of cputable.h

cpu_specs[] is full of #ifdefs depending on the different
types of CPU.

CPUs are mutually exclusive, it is therefore possible to split
cpu_specs[] into smaller more readable pieces.

Create cpu_specs_XXX.h that will each be dedicated on one
of the following mutually exclusive families:
- 40x
- 44x
- 47x
- 8xx
- e500
- book3s/32
- book3s/64

In book3s/32, the block for 603 has been moved in front in order
to not have two 604 blocks.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
[mpe: Fix CONFIG_47x to be CONFIG_PPC_47x, tweak some formatting]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/a44b865e0318286155273b10cdf524ab697928c1.1663606875.git.christophe.leroy@csgroup.eu