wlcore: Make sure firmware is initialized in wl1271_op_add_interface()

We have wl12xx_boot() call wl12xx_enable_interrupts() and if we have
wl1271_op_add_interface() call pm_runtime_get_sync() before the interrupts
are enabled. And then we get the following error during boot:

wlcore: ERROR ELP wakeup timeout!

Let's fix this by first checking if we need to boot the firmware. And
only after that call pm_runtime_get_sync() when interrupts are enabled.
And only after that do the check for wl12xx_need_fw_change().

Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>