can: sun4i_can: Only show Kconfig if ARCH_SUNXI is set

can: sun4i_can: Only show Kconfig if ARCH_SUNXI is set

When adding the RISCV option I didn't gate it behind ARCH_SUNXI.
As a result this option shows up with Allwinner support isn't enabled.
Fix that by requiring ARCH_SUNXI to be set if RISCV is set.

Fixes: 8abb95250ae6 ("can: sun4i_can: Add support for the Allwinner D1")
Reported-by: Geert Uytterhoeven <[email protected]>
Closes: https://lore.kernel.org/linux-sunxi/CAMuHMdV2m54UAH0X2dG7stEg=grFihrdsz4+o7=_DpBMhjTbkw@mail.gmail.com/
Signed-off-by: John Watts <[email protected]>
Reviewed-by: Geert Uytterhoeven <[email protected]>
Link: https://lore.kernel.org/all/[email protected]
Signed-off-by: Marc Kleine-Budde <[email protected]>