[armel] Change MTD and RTC related to modules (fixes FTBFS)

Change MTD_OF_PARTS, MTD_BLOCK, and MTD_PHYSMAP_OF from built-in
to modules.

And, also change all RTC related except RTC_DRV_MV, which includes
RTC_DRV_DS1307, RTC_DRV_RS5C372, RTC_DRV_PCF8563, RTC_DRV_M41T80,
and RTC_DRV_S35390A, to modules. Because most marvell boards use
RTC_DRV_MV.