Kconfig: Refactoring of top-level Kconfig file

Some refactoring of the top-level Kconfig file which includes:

* using "if" to remove numerous identical dependency tests
* reordering config entries to group related ones
* spelling and grammar fixes

There should be no functional changes, only aesthetic ones.

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>