target/arm: Restrict v7A TCG cpus to TCG accel

target/arm: Restrict v7A TCG cpus to TCG accel

KVM requires the target cpu to be at least ARMv8 architecture
(support on ARMv7 has been dropped in commit 82bf7ae84ce:
"target/arm: Remove KVM support for 32-bit Arm hosts").

A KVM-only build won't be able to run TCG cpus, move the
v7A CPU definitions to cpu_tcg.c.

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20210306151801.2388182-1-f4bug@amsat.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>