ARM: 8385/1: VDSO: group link options

Currently the VDSO's link options are kind of a mess spread between

ccflags-y and cmd_vdsold.  Collect linker directives into one
variable, VDSO_LDFLAGS, and use that in cmd_vdsold.

Signed-off-by: Nathan Lynch <nathan_lynch@mentor.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>