sunxi-disp: Fall back to kmalloc-ed mem when no fb mem is reserved

Since it is now possible to disable fb-mem reservation from the cmdline,
enable the kmalloc fallback path even if CONFIG_FB_SUNXI_RESERVED_MEM is set.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
axp20: Don't create the virtual axp devs if pmu_used is not set

This stops dmesg showing these:
[   86.720000] platform reg-20-cs-buck3: Driver reg-20-cs-buck3 requests probe deferral
[   86.720000] platform reg-20-cs-buck2: Driver reg-20-cs-buck2 requests probe deferral
[   86.740000] platform reg-20-cs-ldo4: Driver reg-20-cs-ldo4 requests probe def
<snip more of the same>

Each time a usb device gets (un)plugged when using a generic kernel build
(so with axp20 enabled) on a board without a pmu, such as the mk802, or
the a13_olinuxino_micro.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>