ARM: dts: msm: Add proxy consumer properties for regulators on msm8974

Add regulator proxy consumer properties for the regulators used
by clocks on msm8974 and msm8974pro targets:

     supply     msm8974            msm8974pro
1. vdd_dig    pm8841_s2_corner  pma8084_s2_corner
2. vdd_mem    pm8841_s1_ao      pma8084_s1_ao
3. vdd_hfpll  pm8941_l12        pma8084_l12

Use proxy consumers to ensure that each of these regulators is
kept on during boot-up at the highest allowed voltage.  This
guarantees that any hardware set up by bootloaders at non-minimum
regulator voltage will continue to operate until the driver
responsible for the hardware has initialized and made its own
regulator requests.

Change-Id: Ib7f0356acf3c6625552ef09c888835b749da5d88
Signed-off-by: David Collins <collinsd@codeaurora.org>