Fix building of env_embedded.o

Since commit a706bfc7 common/env_embedded.o and tools/envcrc were
only built when CONFIG_ENV_IS_EMBEDDED was set, but this breaks
building for many boards.

We always have to build these files when CONFIG_ENV_IS_IN_FLASH is
set.

Signed-off-by: Wolfgang Denk <wd@denx.de>