target/hppa: Convert hppa_cpu_init() to ResetHold handler

target/hppa: Convert hppa_cpu_init() to ResetHold handler

hppa_cpu_initfn() is called once when a HPPA CPU instance is
initialized, but it sets fields which should be set each time
a CPU resets. Rename it as a reset handler, having it matching
the ResettablePhases::hold() signature, and register it as
ResettableClass handler.

Since on reset the CPU registers and TLB entries are expected
to be zero, add a memset() call clearing CPUHPPAState up to
the &end_reset_fields marker.

Signed-off-by: Helge Deller <deller@gmx.de>
Co-developed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20241231190620.24442-3-philmd@linaro.org>