Blackfin: merge sram init functions

Now that the sram_init() function exists only to call the bfin_sram_init()
after the punting of the reserve_pda() function, simply merge the two to
avoid pointless overhead.

Signed-off-by: Graf Yang <graf.yang@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>