fwk: only use __access__(none) with GCC 11
GCC 10 onwards supports read_only, write_only and read_write attributes to access and only GCC 11 (which is unreleased at this point in time) also supports none.
To fix the build on GCC 10, only use none with GCC 11.
Change-Id: I65a258fb2fc93874fe0b6fe5e695a6df030ce3a1 Signed-off-by: Ross Burton ross.burton@arm.com