uboot: zynqmp: Support loading a PMU config

uboot: zynqmp: Support loading a PMU config

Before now, U-Boot SPL could only load the Platform Management Unit
(PMU) by patching the board-specific pm_cfg_obj.c file into the generic
PMU firmware, but that then requires generating a new PMU firmware for
every board configuration. To fix that, Luca Ceresoli added support to
U-Boot to load the pm_cfg_obj[1].

Like the PMU firmware, we need a way to pass the PMU cfg to U-Boot
during build. U-Boot only accepts the binary format of the cfg, so we
must convert the source file with the tool provided with U-Boot.

[1] https://lucaceresoli.net/zynqmp-uboot-spl-pmufw-cfg-load/

Signed-off-by: Brandon Maier <brandon.maier@rockwellcollins.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>