mb/system76/oryp6: Drop DIMM_SPD_SIZE

The board uses the default size specified in the SoC.

Change-Id: Ie71a0fea1ff9de6c4f1ce8db2db09bb3cd35d04d
Signed-off-by: Tim Crawford <tcrawford@system76.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/56865
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Reviewed-by:  Felix Singer <felixsinger@posteo.net>

src/mainboard/system76/oryp6/Kconfig

@@ -54,10 +54,6 @@ config DIMM_MAX
 	int
 	default 2
 
-config DIMM_SPD_SIZE
-	int
-	default 512
-
 config VGA_BIOS_ID
 	string
 	default "8086,9bc4"