EDAC/amd64: Split read_mc_regs() into dct/umc functions

Call them from their respective hw_info_get() paths.

ECC symbol size is not needed on UMC systems, so determine_ecc_sym_sz()
is left out of the UMC path. Do not save TOP_MEM* values on modern
controllers because they're not needed there (read: they were used only
for debugging, if anything).

  [ Yazen: rebased/reworked patch and reworded commit message. ]

Signed-off-by: Muralidhara M K <muralidhara.mk@amd.com>
Co-developed-by: Naveen Krishna Chatradhi <naveenkrishna.chatradhi@amd.com>
Signed-off-by: Naveen Krishna Chatradhi <naveenkrishna.chatradhi@amd.com>
Co-developed-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230127170419.1824692-16-yazen.ghannam@amd.com