firmware: arm_scmi: Use the bitmap API to allocate bitmaps

Use devm_bitmap_zalloc() instead of hand-writing them.

It is less verbose and it improves the semantic.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Cristian Marussi <cristian.marussi@arm.com>
Tested-by: Cristian Marussi <cristian.marussi@arm.com>
Link: https://lore.kernel.org/r/c073b1607ada34d5bde6ce1009179cf15bbf0da3.1657308593.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>