target/riscv: Update default priority table for local interrupts

target/riscv: Update default priority table for local interrupts

The latest AIA draft v0.3.0 defines a relatively simpler scheme for
default priority assignments where:
1) local interrupts 24 to 31 and 48 to 63 are reserved for custom use
   and have implementation specific default priority.
2) remaining local interrupts 0 to 23 and 32 to 47 have a recommended
   (not mandatory) priority assignments.

We update the default priority table and hviprio mapping as-per above.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20220616031543.953776-3-apatel@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>