power/sbgemm_kernel_power10.c: reformat to 4-space indentation

Pure cosmetic cleanup; no functional changes.

Convert all tab-indented code to 4-space indent, align macro
continuation backslashes, switch brace placement to consistent K&R
style, reformat multi-line vector initialisers, and remove trailing
whitespace on SAVE4x2_ACC1_SCALAR.

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

Author: amritahs-ibm