AMD southbridge: remove sp5100

AMD southbridge: remove sp5100

Southbridge SP5100 support was compiled with SB700 code, but static
device info structure would use sp5100/chip.h. To solve this drop
support for separate chip sp5100 and adjust the relevant Kconfig
options.

Removes chip directory:
  src/southbridge/amd/sp5100/

Rename Kconfig option
 from: SOUTHBRIDGE_AMD_SP5100
   to: SOUTHBRIDGE_AMD_SUBTYPE_SP5100

Change-Id: I873c6ad3624ee69165da6ab7287dfb7e006ee8e8
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/679
Tested-by: build bot (Jenkins)
Reviewed-by: Zheng Bao <zheng.bao@amd.com>
Reviewed-by: Marc Jones <marcj303@gmail.com>