arm: dts: introduce am62a7 dtbs from linux kernel

Introduce the basic am62a7 SoC dtbs from the v6.1-rc3 tag of the linux
kernel along with the new am62a specific pinmux definition that we will
use to generate the dtbs for the u-boot-spl and u-boot binaries

Co-developed-by: Vignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: Bryan Brattlof <bb@ti.com>