powerpc/powernv: Get L1D flush requirements from device-tree

The device-tree properties no-need-l1d-flush-msr-pr-1-to-0 and
no-need-l1d-flush-kernel-on-user-access are the equivalents of
H_CPU_BEHAV_NO_L1D_FLUSH_ENTRY and H_CPU_BEHAV_NO_L1D_FLUSH_UACCESS
from the H_GET_CPU_CHARACTERISTICS hcall on pseries respectively.

In commit d02fa40d ("powerpc/powernv: Remove POWER9 PVR version
check for entry and uaccess flushes") the condition for disabling the
L1D flush on kernel entry and user access was changed from any non-P9
CPU to only checking P7 and P8.  Without the appropriate device-tree
checks for newer processors on powernv, these flushes are unnecessarily
enabled on those systems.  This patch corrects this.

Fixes: d02fa40d ("powerpc/powernv: Remove POWER9 PVR version check for entry and uaccess flushes")
Reported-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Russell Currey <ruscur@russell.cc>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220404101536.104794-1-ruscur@russell.cc