target/ppc/spapr: Update H_GET_CPU_CHARACTERISTICS L1D cache flush bits

target/ppc/spapr: Update H_GET_CPU_CHARACTERISTICS L1D cache flush bits

There are several new L1D cache flush bits added to the hcall which reflect
hardware security features for speculative cache access issues.

These behaviours are now being specified as negative in order to simplify
patched kernel compatibility with older firmware (a new problem found in
existing systems would automatically be vulnerable).

[dwg: Technically this changes behaviour for existing machine types.
 After discussion with Nick, we've determined this is safe, because
 the worst that will happen if a guest gets the wrong information due
 to a migration is that it will perform some unnecessary workarounds,
 but will remain correct and secure (well, as secure as it was going
 to be anyway).  In addition the change only affects cap-cfpc=safe
 which is not enabled by default, and in fact is not possible to set
 on any current hardware (though it's expected it will be possible on
 POWER10)]

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Message-Id: <20210615044107.1481608-1-npiggin@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>