forked from Mirrors/opensbi

SBI v0.2 specification allows vendor extensions and it should be implemented in a independent of the core sbi library. Introduce a single platform callback that will let platforms handle all vendor extensions in platform specific code if they want. Signed-off-by: Atish Patra <atish.patra@wdc.com> Reviewed-by: Anup Patel <anup.patel@wdc.com>