armv8/armv9: Avoid using -march when -mcpu is chosen

Current include logic goes into generic arm v8/v9 architecture tunes and
adds corresponding -march option after synthesizing it from various tune
fragments, this is fine for a machine which is using armv8/armv9 based
tunes but cortex tunes are intentionally using -mcpu option based on
selected tune value. So when cortex based default tune is selected for a
machine, it will add both -mcpu and -march to the compiler commandline
which can result in invalid combinations for this pair in gcc's own
logic. This can then result in compiler warnings/errors reporting this

e.g.

aarch64-yoe-linux-gcc  -mcpu=cortex-a72.cortex-a53 -march=armv8-a+crc+crypto -mbranch-protection=standard
...
cc1: error: switch '-mcpu=cortex-a72.cortex-a53' conflicts with '-march=armv8-a+crc+crypto' switch and resulted in options '+crc+crypto' being added [-Werror]

This is seen in lot of configure test results in glibc 2.39 and the
warning is promoted to errors by gcc in some of these checks especially
with gcc-14, the logs also show it as warning in other places in
configure checks.

mcpu option will compute relevant march implicitly as it specifies a cpu
implementation and this will be the right value to use, therefore do not
specify -march when -mcpu is already describing the cpu.

(From OE-Core rev: e64f0c1b6ac5d598a79a21de5f3060f83cb9523e)

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Cc: Ross Burton <ross.burton@arm.com>
Cc: Jon Mason <jdmason@kudzu.us>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

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