ARM: dts: msm: specify a PWM mode threshold for BoB on SDM660

Specify a 2 A PWM vs AUTO mode load current threshold for the
BoB regulator.  Also specify the initial mode as AUTO.
Consumer that require the BoB to be in PWM mode should request
2000000 uA or more.

CRs-Fixed: 2054771
Change-Id: I2d2687a9b2204f677818b639fb6650084cffd84a
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>