ARM: dts: msm: add/fix the regulator devices for mpq8092

1. Add the missing PMA8084 LDO 8 regulator device node.
2. Update the voltage constraints, parent supply regulator,
and always-on configuration for all PMA8084 PMIC regulator
devices in order to match the latest MPQ8092 power grid
hardware documentation.

Change-Id: Ie17316044d529a935f24d19c034f448621354a40
Signed-off-by: Srinivas Ramana <sramana@codeaurora.org>