hw/intc/riscv_aplic.c fix non-KVM --enable-debug build

hw/intc/riscv_aplic.c fix non-KVM --enable-debug build

Commit 6df0b37e2ab breaks a --enable-debug build in a non-KVM
environment with the following error:

/usr/bin/ld: libqemu-riscv64-softmmu.fa.p/hw_intc_riscv_aplic.c.o: in function `riscv_kvm_aplic_request':
./qemu/build/../hw/intc/riscv_aplic.c:486: undefined reference to `kvm_set_irq'
collect2: error: ld returned 1 exit status

This happens because the debug build will poke into the
'if (is_kvm_aia(aplic->msimode))' block and fail to find a reference to
the KVM only function riscv_kvm_aplic_request().

There are multiple solutions to fix this. We'll go with the same
solution from the previous patch, i.e. add a kvm_enabled() conditional
to filter out the block. But there's a catch: riscv_kvm_aplic_request()
is a local function that would end up being used if the compiler crops
the block, and this won't work. Quoting Richard Henderson's explanation
in [1]:

"(...) the compiler won't eliminate entire unused functions with -O0"

We'll solve it by moving riscv_kvm_aplic_request() to kvm.c and add its
declaration in kvm_riscv.h, where all other KVM specific public
functions are already declared. Other archs handles KVM specific code in
this manner and we expect to do the same from now on.

[1] https://lore.kernel.org/qemu-riscv/d2f1ad02-eb03-138f-9d08-db676deeed05@linaro.org/

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20230830133503.711138-3-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>