power: reset: qcom-dload-mode: Add support for changing dump mode

Beyond full dump download mode, there is also a minidump download mode
and a dump mode which includes full dump and minidump. Add support for
changing dump mode with /sys/kernel/dload/dload_mode sysfs entry and for
toggling whether a download dump mode is used with msm_enable_dump_mode.

Change-Id: I20248df51e8df55c30c0c4f9c46291697cee189b
Signed-off-by: Elliot Berman <eberman@codeaurora.org>