ARM: 8895/1: visit mach-* and plat-* directories when cleaning

When you run "make clean" for arm, it never visits mach-* or plat-*
directories because machine-y and plat-y are just empty.

When cleaning, all machine, plat directories are accumulated to
machine-, plat-, respectively. So, let's pass them to core- to
clean up those directories.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>