DOC: Add missing description to brute_force parameter.

[jhlegarreta]

Add missing description to the brute_force parameter to the docstrings
of the ndimage.morphology.binary_dilation and
ndimage.morphology.binary_erosion methods.

Also made the origin parameter description come after the one for
border_value to match the method signature.

Resolves #8492.

[jaimefrio]

I took a closer look after seeing your #8492 (comment).

The low level function to call is decided here:

scipy/scipy/ndimage/morphology.py

Line 242 in 68c9294

if iterations == 1:

and the branches are:

if iterations == 1:
    _nd_image.binary_erosion(...)  # the "dumb" erosion function
elif cit and not brute_force:
    _nd_image.binary_erosion2(...)  # the "smart" erosion function
else:
    _nd_image.binary_erosion(...)  # the "dumb" erosion function

So if we wanted to be picky, setting brute_force = True ensures that all iterations will be dumb, while with the default brute_force = False an attempt will be made to be smart, if possible, i.e. if the center of the structuring element is true.

If you want to redo the text, I'll let this sit for a day or two before merging, but I think the current wording is sufficiently accurate.

[jhlegarreta]

@jaimefrio OK, thanks for clarifying this. In light of your explanation, I'd also say that the current wording is sufficient. So ready to be merged.

[jaimefrio]

In it goes then, thanks!