arm64 support

[HashBang173]

The multirom source does not seem to be compatible on compiling flounder (arm64)

An error I get as follows:

target C: multirom <= system/extras/multirom/framebuffer.c
system/extras/multirom/framebuffer.c: In function 'vt_set_mode':
system/extras/multirom/framebuffer.c:95:30: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
r = ioctl(fd, KDSETMODE, (void*) (graphics ? KD_GRAPHICS : KD_TEXT));
^
system/extras/multirom/framebuffer.c: In function 'fb_draw_thread_work':
system/extras/multirom/framebuffer.c:936:33: warning: unused parameter 'cookie' [-Wunused-parameter]
void *fb_draw_thread_work(void *cookie)
^
cc1: some warnings being treated as errors