AGESA S3: Refactor S3 backup store locations in SPI

Prepare code to locate S3 backup from CBFS as a file. Follow-up will
replace remaining use of CONFIG_S3_DATA_POS with cbfs_get_file_content().

Change-Id: I693c41c90e61d1a7c7b10e43c9f264d099c9a400
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/6083
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-by: Dave Frodin <dave.frodin@se-eng.com>
2 files changed