ARCv2: entry: comments about hardware auto-save on taken interrupts

[ Upstream commit 45869eb0c0afd72bd5ab2437d4b00915697c044a ]

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Stable-dep-of: 92e2921eeafd ("ARC: define ASM_NL and __ALIGN(_STR) outside #ifdef __ASSEMBLY__ guard")
Signed-off-by: Sasha Levin <sashal@kernel.org>