target/ppc: Move sync instructions to decodetree

target/ppc: Move sync instructions to decodetree

This tries to faithfully reproduce the odd BookE logic. Note the
e206 check in gen_msync_4xx() is always false, so not carried over.

It does change the handling of non-zero reserved bits outside the
defined fields from being illegal to being ignored, which the
architecture specifies ot help with backward compatibility of new
fields. The existing behaviour causes illegal instruction exceptions
when using new POWER10 sync variants that add new fields, after this
the instructions are accepted and are implemented as supersets of
the new behaviour, as intended.

Reviewed-by: Chinmay Rath <rathc@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>