Fix typos in src/console/Kconfig

Fix typos in src/console/Kconfig

- cash -> Cache
- make the new size of the cbmem console buffer the default

Change-Id: Ia906077257e93622ad56bc54a42f8184ade78b29
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/726
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>