cpu: tcg_ops: move to tcg-cpu-ops.h, keep a pointer in CPUClass

cpu: tcg_ops: move to tcg-cpu-ops.h, keep a pointer in CPUClass

we cannot in principle make the TCG Operations field definitions
conditional on CONFIG_TCG in code that is included by both common_ss
and specific_ss modules.

Therefore, what we can do safely to restrict the TCG fields to TCG-only
builds, is to move all tcg cpu operations into a separate header file,
which is only included by TCG, target-specific code.

This leaves just a NULL pointer in the cpu.h for the non-TCG builds.

This also tidies up the code in all targets a bit, having all TCG cpu
operations neatly contained by a dedicated data struct.

Signed-off-by: Claudio Fontana <[email protected]>
Message-Id: <20210204163931[email protected]>
Signed-off-by: Richard Henderson <[email protected]>