This option has a bool type, not hex.
Fix it and enable it if CONFIG_DM is on because Driver Model always
requires malloc memory. Devices are scanned twice, before/after
relocation. CONFIG_SYS_MALLOC_F should be enabled to use malloc
memory before relocation. As it is board-independent, handle it
globally.

Signed-off-by: Masahiro Yamada
Acked-by: Stephen Warren
Reviewed-by: Simon Glass
Acked-by: Robert Baldyga