ipq806x: 5.15: drop arm override compile patch

ipq806x: 5.15: drop arm override compile patch

Drop arm override compile patch. The use is dubious and at times (2016)
it was never explained why this was required.
Krait CPU and Cortex-a15 may be similar but they have some intrinsic
difference. While very similar they differ a lot in additional feature
and also cache configuration.

Also these conflict with raid6 libraty compilation that use specific
workaround not compatible with cortex-a15 and produce compilation
warning.
Fix compilation warning:
cc1: error: switch '-mcpu=cortex-a15' conflicts with switch '-march=armv7-a+simd' [-Werror]
cc1: all warnings being treated as errors

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>