[arm] Specify +dotprod support for Cortex-A55 and Cortex-A75 in native system detection

[arm] Specify +dotprod support for Cortex-A55 and Cortex-A75 in native system detection

Since support for -mcpu=cortex-a55 and -mcpu=cortex-a75
was added we added support for the +dotprod extension
which these CPUs support.

We already specify as such in the arm-cpus.in entries for
these processors. However the table in driver-arm.c was
not adding +dotproct to the -march string that it generates.

This patch fixes that oversight.
In the future I'd like to get the arm_cpu_table in driver-arm.c
be auto-generated somehow from the arm-cpus.in data so
that we don't have to keep track of discrepancies explicitly...

Bootstrapped and tested on arm-none-linux-gnueabihf.

	* config/arm/driver-arm.c (arm_cpu_table): Specify dotprod
	support for Cortex-A55 and Cortex-A75.

From-SVN: r255943