lib: Simplify sbi_platform early_init() and final_init() hooks

Instead of having separate early_init() and final_init() hooks
for cold and warm boot, this patch updates struct sbi_platform
to have just one early_init() and one final_init() hook. The
type of boot (cold or warm) is now a boolean flag parameter for
the updated early_init() and final_init() hooks.

Signed-off-by: Anup Patel <anup.patel@wdc.com>