target/riscv/kvm: Replace legacy cpu_physical_memory_read/write() calls

target/riscv/kvm: Replace legacy cpu_physical_memory_read/write() calls

Commit b7ecba0f6f6 ("docs/devel/loads-stores.rst: Document our
various load and store APIs") mentioned cpu_physical_memory_*()
methods are legacy, the replacement being address_space_*().

Since the SBI DBCN is handled within a vCPU context, use its
default address space. Replace using the address space API.
As with the previous implementation, ignore whether the memory
accesses succeeded or failed.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Message-Id: <20251002145742.75624-4-philmd@linaro.org>