ARM: dts: msm: update configurations of gfx_cpr regulator for 8996AU CDP

Halo HL7509 external buck converter powers VDD_GFX voltage rail
on 8996 automotive CDP. Specify the necessary configuration for
it.

Disable closed-loop CPR operation for graphics CPR controller
until it is verified with this external buck configuration.

CRs-Fixed: 978343
Change-Id: I7d9bdce4c0b381942c6201f80b0970cad8d82ab5
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>