firmware: ti_sci: Use devm_bitmap_zalloc when applicable

'xfer_alloc_table' is a bitmap. So use 'devm_bitmap_zalloc()' to simplify
code and improve the semantic of the code.

While at it, remove a redundant 'bitmap_zero()' call.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Nishanth Menon <nm@ti.com>
Link: https://lore.kernel.org/r/43ab1a7dd073d0d037d5d4bbbd5f8335de605826.1667457664.git.christophe.jaillet@wanadoo.fr