habanalabs: replace 'pf' to 'prefetch'

pf was an abbreviation for prefetch but because pf already stands
for 'physical function', we decided to change it to 'prefetch'.

Signed-off-by: Dafna Hirschfeld <dhirschfeld@habana.ai>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>