soc: qcom: mdt_loader: Use request_firmware_into_buf()

By switching to the request_firmware_into_buf() we load the segment data
straight into the preallocated buffers, reducing the need for allocating
scratch buffers for these. In particular the modem firmware consists of
multiple segments in the range 5-15MB, making this worth while.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>