Add proper defaults for IxMIN/IxMAX kernels

the fallbacks from Makefile.L1 assume a combined source for absolute value and non-absolute (with ifdef USE_ABS) but here we have separate implementations

kernel/power/KERNEL

@@ -50,3 +50,26 @@ ifndef DSDOTKERNEL
 DSDOTKERNEL = ../generic/dot.c
 endif
 
+ifndef ISMINKERNEL
+ISMINKERNEL = imin.S
+endif
+
+ifndef IDMINKERNEL
+IDMINKERNEL = imin.S
+endif
+
+ifndef IQMINKERNEL
+IQMINKERNEL = imin.S
+endif
+
+ifndef ISMAXKERNEL
+ISMAXKERNEL = imax.S
+endif
+
+ifndef IDMAXKERNEL
+IDMAXKERNEL = imax.S
+endif
+
+ifndef IQMAXKERNEL
+IQMAXKERNEL = imax.S
+endif