QcomModulePkg: Library: Decrease the writing unit for parallel download

The big image buffer may take a long flashing time which will block
parallel usb image download. For example, if the write speed is 50MB/s,
256MB buffer may take more than 5 senconds. It will cause the fastboot
protocol host side timeout. So split the image into small writing units
to let usb have chance to champ in and doing work in parallel.

Change-Id: I68d57fb08efb7f3899d38de929ce133d3c3f6fb3
3 files changed