ramips/rt288x,rt3883: fix IMAGE_SIZE for all devices

ramips/rt288x,rt3883: fix IMAGE_SIZE for all devices

This fixes IMAGE_SIZE for all devices based on the partition size
given in DTS:

DEVICE                 *.MK    *.DTS      VERDICT
airlink101_ar670w      (4M)    0x3c0000   wrong
airlink101_ar725w      -       0x3B0000   wrong
asus_rt-n15            (4M)    0x3b0000
belkin_f5d8235-v1      7744k   0x7b0000   wrong
buffalo_wli-tx4-ag300n (4M)    0x3b0000
buffalo_wzr-agl300nh   (4M)    0x3b0000
dlink_dap-1522-a1      3801088 0x3a0000
ralink_v11st-fe        (4M)    0x003b0000

asus_rt-n56u           -       0x007b0000 default
belkin_f9k1109v1       7224k   0x7a0000   wrong
dlink_dir-645          -       0x7b0000   default
edimax_br-6475nd       7744k   0x00790000
loewe_wmdr-143n        -       0x7b0000   default
omnima_hpm             16064k  0x00fb0000
samsung_cy-swr1100     -       0x7b0000   default
sitecom_wlr-6000       7244k   0x713000
trendnet_tew-691gr     -       0x007b0000 default
trendnet_tew-692gr     -       0x007b0000 default

No verdict means that the device is correctly set.

Legend:
( ): Value is set via ralink_default_fw_size_xxM
[ ]: Value is derived from parent definition
 - : Value is not set and derived from default definition

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>