net: dsa: bcm_sf2: Do not rely on kexec_in_progress

After discussing with Eric, it turns out that, while using
kexec_in_progress is a nice optimization, which prevents us from always
powering on the integrated PHY, let's just turn it on in the shutdown
path.

This removes a dependency on kexec_in_progress which, according to Eric
should not be used by modules

Fixes: 2399d614 ("net: dsa: bcm_sf2: Prevent GPHY shutdown for kexec'd kernels")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>