Power10: Replace vector pair loads with __builtin_vsx_lxvp

Replace normal vector pair pointer dereferences with the optimized
__builtin_vsx_lxvp builtin across DGEMM, ZGEMM, and DGEMV kernels.

Also done some identation corrections in dgemm_kernel_power10.c.
This is done as part of POWER code cleanup and may not have any
performance impact.

Signed-off-by: Amrita H S <amritahs@linux.vnet.ibm.com>

Author: amritahs-ibm