bcm53xx: update copy of ASM entry flushing whole D-cache

Previous version was based on code from kernel 2.6.22 with Broadcom two
trivial modifications. This updates the copy to the version from current
kernel and refreshes the patch.

This was tested for regressions on Netgear R6250 (BCM4708A0), D-Link
DIR-885L (BCM4709C0) and Tenda AC9 (BCM47189B0).

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>