platform: kendryte/k210: Use new mechanism of builtin DTB

We update kendryte/k210 to use new mechanism of having builtin DTB
where we convert k210.dts to C source and further compile-n-link it
with libplatsbi.a.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>