ARM: dts: dra72: Add separate dtsi for tps65917

dra72-evm-common.dtsi consolidates dra72-evm.dts and dra72-evm-revc.dts
which also include tps65917 pmic support as both the evms uses the same
pmic. But, dra71-evm has mostly similar features with a different pmic.
In order to exploit dra72-evm-common.dtsi, creating a separate dtsi
for tps65915 support and including it in respective board files.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>