When running in M-mode we can't use SBI based drivers.  Add a new
CONFIG_RISCV_SBI that drivers that do SBI calls can depend on
instead.
Signed-off-by: NDamien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: NAnup Patel <anup@brainfault.org>
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NPaul Walmsley <paul.walmsley@sifive.com>