hw/mips: implement ITC Storage - P/V Sync and Try Views

hw/mips: implement ITC Storage - P/V Sync and Try Views

P/V Synchronized and Try Views can be used to access Semaphore cells.
Load returns current value and post-decrements the value in the cell
(until it reaches zero). Stores increment the value (until it saturates
at 0xFFFF).

P/V Synchronized View causes the issuing thread to block on read if value
is 0. P/V Try View does not block the thread, it returns 0 in this case.

Cell's Empty and Full bits are not modified.

Trap bit (i.e. Gating Storage exceptions) not implemented.

Signed-off-by: Leon Alrae <leon.alrae@imgtec.com>