remoteproc: elf_loader: Always check the validity of the image before loading

rproc_elf32_load_image() rely on user to send a valid address for elf loading.
Instead do a sanity check on the address passed by user. This will help
all rproc elf users to not call sanity_check explicitly before calling
elf_loading.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Reviewed-by: Fabien Dessenne <fabien.dessenne@st.com>