powerpc/mm/book3s/hash: Rename flush_tlb_pmd_range

This function does the hash page table update. Hence rename it to
indicate this better to avoid confusion with flush_pmd_tlb_range()

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
[mpe: Drop unnecessary extern]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220907081941.209501-1-aneesh.kumar@linux.ibm.com