Kconfig: Hide DYNAMIC_CBMEM.

Only one setting actually works (exact value depends on board). So
no need to show it.

Change-Id: I2a85719264bbac07791ef6a9279590ba768c309e
Signed-off-by: Vladimir Serbinenko <phcoder@gmail.com>
Reviewed-on: http://review.coreboot.org/7359
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Tested-by: build bot (Jenkins)
2 files changed