The smallest stm32f0 has 4k sram, so use this as the default.
Change-Id: I9097be9608da92b1b9da504e5bacc1280c86907a
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/603
Tested-by: jenkins
Reviewed-by: Freddie Chopin <freddie.chopin@gmail.com>