msm: peripheral-loader: Change IOMAP_SIZE from SZ_4M to SZ_1M

The ioremap call made for zeroing out trailing memory is currently
requesting for a 4M memory region. This is resulting in vmalloc
allocation failures on some platforms.
Instead, request for 1M memory locations and zero out the area
in smaller chunks to make this failure less probable.

Signed-off-by: Deepak Katragadda <dkatraga@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>