powerpc/configs: Disable legacy ptys on microwatt defconfig

We shouldn't need legacy ptys, and disabling the option improves boot
time by about 0.5 seconds.
Signed-off-by: Anton Blanchard <anton@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210805112005.3cb1f412@kryten.localdomain

arch/powerpc/configs/microwatt_defconfig

@@ -57,6 +57,7 @@ CONFIG_NETDEVICES=y
 # CONFIG_INPUT is not set
 # CONFIG_SERIO is not set
 # CONFIG_VT is not set
+# CONFIG_LEGACY_PTYS is not set
 CONFIG_SERIAL_8250=y
 # CONFIG_SERIAL_8250_DEPRECATED_OPTIONS is not set
 CONFIG_SERIAL_8250_CONSOLE=y