powerpc/include: Remove mpc8260.h and m82xx_pci.h

SIU_INT_IRQ1 is not used anywhere and __IO_BASE is defined in
asm/io.h

Remove m82xx_pci.h

Then the only thing remaining in mpc8260.h is MPC82XX_BCR_PLDP

Move MPC82XX_BCR_PLDP into asm/cpm2.h then remove mpc8260.h

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/afe23bf3624c389ff17e9789884c78c124b7b202.1691474658.git.christophe.leroy@csgroup.eu