firmware: ti_sci: 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>
Signed-off-by: Nishanth Menon <nm@ti.com>
Link: https://lore.kernel.org/r/3ee11e9e83f7c1552d237f5c28f554319fcbbf1f.1657308216.git.christophe.jaillet@wanadoo.fr