Don't sync the I/D caches when they are coherent

In the arm64 loader we need to syncronise the I and D caches. On some
newer CPUs the I and D caches are coherent so we don't need to perform
these operations.

While here remove the arguments to cpu_inval_icache as they are unneeded.

Reported by: cperciva
Tested by: cperciva
Sponsored by: Innovate UK