io_dummy: correct sparse warnings
io_dummy: correct sparse warnings

Include io_dummy.h header file.
Use static for device_type_dummy function.

Signed-off-by: Yann Gautier <e753f6969c288905606e3c07464886d4f1fc1be0@st.com>
Signed-off-by: Etienne Carriere <f21bc5b8f3ea1962eb45af359f1abea6578cab94@st.com>

lsigithub/arm-trusted-firmware_public,achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware,lsigithub/arm-trusted-firmware_public