EDAC/mc: Split edac_mc_alloc() into smaller functions

edac_mc_alloc() is huge. Factor out code by moving it to the two new
functions edac_mc_alloc_csrows() and edac_mc_alloc_dimms(). Do not
move code yet for better review.

 [ bp: sort local args in reversed fir tree order. ]

Signed-off-by: Robert Richter <rrichter@marvell.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Aristeu Rozanski <aris@redhat.com>
Link: https://lkml.kernel.org/r/20200123090210.26933-2-rrichter@marvell.com