docs/system/arm/virt.rst: Improve 'highmem' option docs

Improve the 'highmem' option docs to note that by default we assume
that a 32-bit kernel on an LPAE-capable CPU has LPAE enabled, and
what the consequences are.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Message-id: 20240109170834.1387457-1-peter.maydell@linaro.org
1 file changed