rockchip: dts: rk3399-puma: put EFI partition entries at 2MB

When creating a EFI/GUID partition map for the RK3399-Q7 through
U-Boot, the partition entries should be places at a 1MB offset from
the start of the device to give us space for the environment (at 16KB
on SD/MMC devices), the SPL stage (at 32KB on SD/MMC devices) and the
image payload (at 256KB on SD/MMC devices).

This change sets this up through the u-boot,efi-partition-entries-offset
/config property in the RK3399-Q7 DTSI.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>