Changed _DOUBLE_IN_TWO_REGISTERS flag to _BIG_IN_TWO_REGISTERS

Now this flag has the meaning that both double and int64 values are to be
held in a pair of registers.
Also set param_type for int and int64 variables
mips: implement loadq and storeq for int64
mips: implement swapq
mips: renamed a rule function according to name of rule
fixup! mips: special case in load and store rules for float variables
mips: add emit functions for srav
mips: add support for non-const shift in shrsl
mips: add int64 support to copyq
mips: implemented loadpq
mips: let swapq handle doubles