rpi: tizen-boot: rpi3-32b: pass network arguments on flash mode

rpi: tizen-boot: rpi3-32b: pass network arguments on flash mode

To setup network environment for flash manager, this patch makes
passing parameters such as 'ipaddr', 'netmask', and 'gateway' through
kernel bootcmd. Those parameters can be assigned by user-self before
using flash mode.

Note: this is applying below patches from rpi3 to rpi3-32b:
f6f75b5bb37d ("rpi: tizen-boot: rpi3: pass network arguments on flash mode")
e2e0f18b9f3e ("rpi: tizen-boot: rpi3: remove dhcp as default network configuration")

Change-Id: I8de2c8f26f0a5c276ac32e46a83d8fc71eb1e7fd
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>