If you want a depth in Spanish, then you need twelve credits in Spanish. If you're pursuing a bachelor's degree, then at least three credits in Spanish must be at the upper level. The credits need to be in Spanish, but don't necessarily have to be in Spanish literature. An upper level course in Spanish language would also fulfill the requirement.
To put things into perspective, I had a depth in French, which consisted of the following:
Elementary French I (4 credits, lower level)
Elementary French II (4 credits, lower level)
Intermediate French (4 credits, lower level)
French Grammar and Composition (3 credits, upper level)
My upper level course was not a literature course, but it was still a French course so it counted.
Here are some options for upper level Spanish courses.
Brigham Young University
BYU Independent Study - Distance Education Courses - Online Learning
SPAN 441 Survey of Spanish Literature
The University of Wisconsin
Distance Learning Wisconsin Course Search Results
U912-311 Advanced Language Practice
U912-324 Elementary Survey of Spanish Literature: 19th & 20th Centuries
U912-407 Miguel de Unamuno
U912-322 Survey of Literature 12th to 18th Centuries
U912-326 Survey of Spanish American Literature
Another option (and probably the least expensive choice) is to just take an exam for all the credit you need. Either the ACTFL or the NYU Proficiency Exam can result in credit up through the upper level. Some of these credits will duplicate the CLEP, so if you choose one of these options, you'll probably just want to skip the CLEP altogether.