scripts: kconfig: merge_config.sh: use awk in checks too

scripts: kconfig: merge_config.sh: use awk in checks too

Converting from shell/sed/grep loop to awk improves runtime
checks of Yocto genericarm64 kernel config from 20 seconds
to under 1 second. The checks catch this kind of issues:

WARNING: CONFIG_BLK_DEV_DM differs:
Requested value: CONFIG_BLK_DEV_DM=y
Actual value:    CONFIG_BLK_DEV_DM=m
WARNING: CONFIG_SECURITY_NETWORK differs:
Requested value: CONFIG_SECURITY_NETWORK=n
Actual value:    CONFIG_SECURITY_NETWORK=y
WARNING: Value requested for CONFIG_ARM64_BTI_KERNEL not in final .config
Requested value: CONFIG_ARM64_BTI_KERNEL=y
Actual value:

Signed-off-by: Mikko Rapeli <mikko.rapeli@linaro.org>
Link: https://patch.msgid.link/20260122105751.2186609-2-mikko.rapeli@linaro.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>