Platform/RISC-V: Add debug message to SecMain.c

Add more debug messages when search FFS in SEC phase.

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