cxgb4: Use the bitmap API to allocate bitmaps

Use bitmap_zalloc()/bitmap_free() instead of hand-writing them.

It is less verbose and it improves the semantic.

While at it, remove a useless bitmap_zero(). The bitmap is already zeroed
when allocated.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/8a2168ef9871bd9c4f1cf19b8d5f7530662a5d15.1656866770.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Paolo Abeni <pabeni@redhat.com>