Mkimage

as we provide only uefi boot images on releases.openelec.tv please consider the following:
- I have not yet seen a x86_64 hardware where an uefi image doesnt boot. this PR forces "make image" to always produce efi (hybrid, they boot on non-uefi hardware, too) images. 
- so far 'live' mode is available only when booting in legacy mode, but is quite useless because
-- /storage cant be resized at all on gpt partitioned images. this PR completely removes /storage on x86
-- /storage is only 32MB. this PR uses /storage as tmpfs on x86

my personal opinion that "live" mode should not be persistent. it's intended for a quick check if user's hardware (gpu, whatever) is supported, and whether OE can boot at all. with this PR there is "boot: " prompt shown, and one can type "live" in to boot in live mode.