arch: give the choice "Cache type" a name

Give the choice a name so that the soc/board developers can change the
default selection in their Kconfig.*.

For example:
choice CACHE_TYPE
	default HAS_EXTERNAL_CACHE
endchoice

There was a similar issue had beed discussed:
https://github.com/zephyrproject-rtos/zephyr/issues/6948

Signed-off-by: Dylan Hung <dylan_hung@aspeedtech.com>
Change-Id: I07c3e78a5243b30912f8e44fa3181fa163016318
1 file changed