Add rk30sdk to flash.sh

Change-Id: Ie3c34d97513f93f5046fe593eceadde2e2ee656c
rk30sdk: change build variant to userdebug

Change-Id: I0f948b359a6c7fafbbd525e7f09552934f14f89e
If gdb 4.7 is not found, fall back to gdb 4.6

Change-Id: I8a40855d42428372ca980b5955513721c12a8ca0