target/alpha: Replace legacy ld_phys() -> address_space_ld()

target/alpha: Replace legacy ld_phys() -> address_space_ld()

Prefer the address_space_ld/st API over the legacy ld_phys()
because it allow checking for bus access fault.

Since we removed the last legacy uses of the legacy ldst_phys()
API, set the TARGET_NOT_USING_LEGACY_LDST_PHYS_API variable to
hide the legacy API to alpha binaries, avoiding further API uses
to creep in.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20251224160040.88612-7-philmd@linaro.org>