Boosting back to native -mtune=cortex-a15, -march=armv7-a, and -mfpu=neon due to new toolchain

Signed-off-by: Hieu Phan <aznrice2k4@gmail.com>
Revert "drivers/slimbus/slimbus.c: avoid ICE -Og rather than -Os"

This reverts commit 86647f3de8f0d120ee556126cc1d6d399e0ff0df.

Signed-off-by: Hieu Phan <aznrice2k4@gmail.com>
drivers/slimbus/slimbus.c: fix warning: 'tid' may be used uninitialized in this function [-Wmaybe-uninitialized]

Signed-off-by: Hieu Phan <aznrice2k4@gmail.com>