soc: qcom: mdt_loader: Reorder parts of __qcom_mdt_load()

Move the traversal of the program headers to the start of the function,
to make sure that min_ and max_addr are in scope as the call to
qcom_scm_pas_mem_setup() is moved in the next commit.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>