platform: Add AE350 cache control SBIs

This patch contains the following AE350 specific SBIs:

- get mcache_ctl status
- get mmisc_ctl status
- set mcache_ctl status
- set mmisc_ctl status
- I-cache operation
- D-cache operation
- enable/disable L1-I-cache prefetch
- enable/disable L1-D-cache prefetch
- enable/disable non-blocking load store
- enable/disable write-around

Signed-off-by: Nylon Chen <nylon7@andestech.com>
Reviewed-by: Anup Patel <Anup.Patel@wdc.com>
Reviewed-by: Atish Patra <Atish.Patra@wdc.com>