RISC-V: Select APLIC and IMSIC drivers

The QEMU virt machine supports AIA emulation and we also have
quite a few RISC-V platforms with AIA support under development
so let us select APLIC and IMSIC drivers for all RISC-V platforms.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>