toolchain-external: fix visibility and length of Linaro toolchain comment

Maxime Ripard reported that the Linaro toolchains were not visible
when selecting a Cortex-A, but forgetting to set the EABI to
EABIhf. While this is expected, Buildroot should normally should a
comment in this case. However, the comment is only visible when the
selected ARM architecture is not ARMv7 *and* the EABI is not
EABIhf. Instead, make the comment visible when either the selected
architecture is not ARMv7 *or* when the selected EABI is not EABIhf.

While we're at it, reword the comment text so that it actually fits
within the limits of the menuconfig screen.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reported-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Cc: Maxime Ripard <maxime.ripard@free-electrons.com>