riscv: alternatives: Drop the underscores from the assembly macro names

The underscores aren't needed because there isn't anything already
named without them and the _CFG extension. This is a bit of a cleanup
by itself, but the real motivation is for a coming patch which would
otherwise need to add two more underscores to these macro names,
i.e. ____ALTERNATIVE_CFG, and that'd be gross.

Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20221129150053.50464-4-ajones@ventanamicro.com


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>