ipq40xx: fix hard_config partition size on MikroTik hAP-ac2

ipq40xx: fix hard_config partition size on MikroTik hAP-ac2

The routerbootparts driver dynamically discovers the location of MikroTik
partitions, but it cannot determine their size (except by extending them
up to the start of the next discovered partition).

The hard_config partition has a default size of 0x1000 in the driver,
while it actually takes 0x2000 on the hAP-ac2.  Set the correct size in
the hAP-ac2 DTS.

On most devices, this isn't a problem as the actual data fits in 0x1000
bytes.  However, some devices have larger data that doesn't fit in 0x1000
bytes.  In any case, all devices seen so far have enough space for a
0x2000 hard_config partition before the start of the dtb_config partition.
With the current 0x1000 size:

0x00000000e000-0x00000000f000 : "hard_config"
0x000000010000-0x000000017bbc : "dtb_config"

With this patch extending the size to 0x2000:

0x00000000e000-0x000000010000 : "hard_config"
0x000000010000-0x000000017bbc : "dtb_config"

Other ipq40xx boards may need the same fix but it needs testing.

References: https://forum.openwrt.org/t/support-for-mikrotik-hap-ac2/23333/324
Acked-by: Thibaut VARÈNE <hacks@slashdirt.org>
Signed-off-by: Baptiste Jonglez <git@bitsofnetworks.org>