RISC-V: Use RISC-V PeiCoreEntryPoint library

1. Use RISC-V PeiCoreEntryPoint library instance for opensbi
   to switch to the next phase with arg0 as HART Id and arg1
   as the SEC to PEI handoff data.
2. Introduce EDK2 opensbi platform operation functions.
   With this, OEM can has its won platform initialization code
   before and/or after opensbi vendor platform functions.

Cc: Sunil V L <sunilvl@ventanamicro.com>
Cc: Daniel Schaefer <daniel.schaefer@hpe.com>
Signed-off-by: Abner Chang <abner.chang@hpe.com>
Reviewed-by: Daniel Schaefer <daniel.schaefer@hpe.com>
Reviewed-by: Sunil V L <sunilvl@ventanamicro.com>