lib: sbi_ecall: Remove mcause, scratch and hartid parameters

We remove mcause, scratch and hartid parameters from various
functions for ecall handling because we can always get current
HART id and current scratch pointer using just one CSR access.

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