Update sdlatomic.inc according to code style guidelines

[Free-Pascal-meets-SDL-Website]

To be in accordance with the code style guidelines, which states to stay as close as possible with the C code, I would suggest the following updates for sdlatomic.inc:

Line 42: Rename TSDL_Atomic into TSDL_atomic_t and lower-case Value + also adapt all parameter lists consequently Line 49 + 87: Rename param. list (oldValue into oldval, ...) Many param lists: Rename atomic by a and value by v.