powerpc/mpc85xx: Enabling CPC conditionally based on hwconfig options

powerpc/mpc85xx: Enabling CPC conditionally based on hwconfig options

If hwconfig does not contains "en_cpc" then by default all cpcs are enabled
If this config is defined then only those individual cpcs which are defined
in the subargument of "en_cpc" will be enabled e.g en_cpc:cpc1,cpc2; (this
will enable cpc1 and cpc2) or en_cpc:cpc2; (this enables just cpc2)

Signed-off-by: Shaveta Leekha <[email protected]>
Signed-off-by: Sandeep Singh <[email protected]>
Reviewed-by: York Sun <[email protected]>