qualcommax: ipq50xx: upgrade SMEM dualboot Linksys devices

qualcommax: ipq50xx: upgrade SMEM dualboot Linksys devices

Add support for upgrades on dual firmware Linksys devices with the
partition table stored in SMEM and that store both the kernel and rootfs
in a single partition. Switching the active boot partition requires
updating the partition info table in SMEM in addition to setting
the active boot partition in a U-boot variable as U-boot will keep them
in sync upon reboot if they're not.

U-boot always sets the name of the active partition to rootfs and that
of the inactive partition to rootfs_1 in SMEM. when Linux loads the
partition table from SMEM it will load the right partition based on the
offset set in the SMEM partition table. For upgrades, flashing to the
alternate partition will always be to rootfs_1, while flashing the
current partition will be on rootfs.

Signed-off-by: George Moussalem <george.moussalem@outlook.com>
Link: https://github.com/openwrt/openwrt/pull/21038
Signed-off-by: Robert Marko <robimarko@gmail.com>