broadcom: Fix slice memory allocation logic for compressed textures

broadcom: Fix slice memory allocation logic for compressed textures

Compressed textures require their width and height padding to be
calculated based on the number of blocks in the image. This change ensures
that the number of blocks in the texture is a POT for mip levels > 1.

Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23133>