powerpc/ps3: Set CONFIG_UEVENT_HELPER=y in ps3_defconfig

Set CONFIG_UEVENT_HELPER=y in ps3_defconfig.

commit 1be01d4a (driver: base: Disable
CONFIG_UEVENT_HELPER by default) disabled the CONFIG_UEVENT_HELPER option
that is needed for hotplug and module loading by most older 32bit powerpc
distributions that users typically install on the PS3.

Signed-off-by: Geoff Levand <geoff@infradead.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/410cda9aa1a6e04434dfe1f9aa2103d0694f706c.1585340156.git.geoff@infradead.org