irqchip/riscv-aplic: Add support for MSI-mode

The RISC-V advanced platform-level interrupt controller (APLIC) has
two modes of operation: 1) Direct mode and 2) MSI mode.
(For more details, refer https://github.com/riscv/riscv-aia

)

In APLIC MSI-mode, wired interrupts are forwared as message signaled
interrupts (MSIs) to CPUs via IMSIC.

Extend the existing APLIC irqchip driver to support MSI-mode for
RISC-V platforms having both wired interrupts and MSIs.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Björn Töpel <bjorn@rivosinc.com>
Reviewed-by: Björn Töpel <bjorn@rivosinc.com>
Link: https://lore.kernel.org/r/20240307140307.646078-8-apatel@ventanamicro.com