x86: Configure premem cbmem console size

Sometime preram cbmem logs are truncated due to lack of
space (default preram cbmem console size is 0xc00).

Provide Kconfig option to configure preram cbmem console
size so that mainboard can configure it to required value.

Change-Id: I221d9170c547d41d8bd678a3a8b3bca6a76ccd2e
Signed-off-by: Naresh G Solanki <naresh.solanki@intel.com>
Reviewed-on: https://review.coreboot.org/17839
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
diff --git a/src/arch/x86/car.ld b/src/arch/x86/car.ld
index c221fb8..9236009 100644
--- a/src/arch/x86/car.ld
+++ b/src/arch/x86/car.ld
@@ -36,7 +36,7 @@
 	 * in size. Therefore place them at the beginning .car.data section
 	 * so that multiple stages (romstage and verstage) have a consistent
 	 * link address of these shared objects. */
-	PRERAM_CBMEM_CONSOLE(., (CONFIG_LATE_CBMEM_INIT ? 0 : 0xc00))
+	PRERAM_CBMEM_CONSOLE(., (CONFIG_LATE_CBMEM_INIT ? 0 : CONFIG_PRERAM_CBMEM_CONSOLE_SIZE))
 	_car_relocatable_data_start = .;
 	/* The timestamp implementation relies on this storage to be around
 	 * after migration. One of the fields indicates not to use it as the