NOTE: I didn't switch to the new functions in the kernel because for
some reason we get a page fault when trying to fetch the first
instruction of set_timer(addi sp, sp, -48). I doubt this is related to
the set_timer funcion itself and is instead some kind of paging or
linking problem because it works fine with paging disabled and really
just doesnt make sense.
Added legacy extension
Fixed typing memes by just define a sbiword_t typedef
Renamed sbiret_t to SbiRet, I think i'll only use _t for typedefs
Added ecall() variant that takes no additional arguments
Moved opensbi includes to includes/opensbi/...
kernel.cpp uses the legacy extensions instead of raw ecalls
All legacy extension calls are marked as deprecated
