blackfin: update defconfig for bf527-ezkit

To fix compile error:
drivers/usb/musb/blackfin.h:51:3: error: #error "Please use PIO mode in MUSB
driver on bf52x chip v0.0 and v0.1"
make[4]: *** [drivers/usb/musb/blackfin.o] Error 1

Signed-off-by: Bob Liu <lliubbo@gmail.com>