[RISCV] Add tune features of preferred function/loop align

D144048 has added preferred function and loop alignment to
RISCVSubtarget, but now we need to set them manually for
different processors.

Tune features that set preferred function/loop align to
[2, 64] bytes (align 1 is not here since the min align is 2)
are added. These features can be used in processor
definitions.

Reviewed By: asb

Differential Revision: https://reviews.llvm.org/D157832