target/arm/hvf: sign extend the data for a load operation when SSE=1

target/arm/hvf: sign extend the data for a load operation when SSE=1

In the syndrome value for a data abort, bit 21 is SSE, which is
set to indicate that the abort was on a sign-extending load. When
we handle the data abort from the guest via address_space_read(),
we forgot to handle this and so would return the wrong value if
the guest did a sign-extending load to an MMIO region. Add the
sign-extension of the returned data.

Cc: qemu-stable@nongnu.org
Signed-off-by: Joelle van Dyne <j@getutm.app>
Message-id: 20250224184123.50780-1-j@getutm.app
[PMM: Drop an unnecessary check on 'len'; expand commit message]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>