sim: Fix MCUBOOT_SWAP_USING_SCRATCH defined in direct-xip and ram-load

When 'direct-xip' or 'ram-load' features were enabled,
CONFIG_BOOT_SWAP_USING_SCRATCH and MCUBOOT_SWAP_USING_SCRATCH were
defined even though swap using scratch wasn't used. This commit fixes
the issue.

Signed-off-by: Thomas Altenbach <thomas.altenbach@legrand.com>