soc: qti_battery_debug: Move qbg_context to device bin file

Replace the "qbg_context" debugfs blob with a binary file associated
with the battery_debug device that provides the same functionality as
the existing debugfs blob for getting QBG context.

Usage:
  # cd /sys/devices/platform/soc/soc:qcom,pmic_glink_log/\
    soc:qcom,pmic_glink_log:qcom,battery_debug
  # echo 1 > qbg_context
  # cat qbg_context > file.bin

Change-Id: I59cfea2880362a95d8c87c02b4d823bfdca4e1e2
Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org>