powerpc/chrp: Add __init attribute to eligible functions

The function `Enable_SRAM` defined in 'arch/powerpc/platforms/chrp' is
deserving of an `__init` macro attribute. This function is only called by
other initialization functions and therefore should inherit the attribute.

Signed-off-by: Nick Child <nick.child@ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211216220035.605465-9-nick.child@ibm.com