sh: Remove CONFIG_VSYSCALL reference from UAPI

sh: Remove CONFIG_VSYSCALL reference from UAPI

AT_SYSINFO_EHDR defines the auxvector index representing the vDSO
entrypoint. Its value or presence does not depend on whether a vDSO
is actually provided by the kernel.

The definition of AT_SYSINFO_EHDR was gated between CONFIG_VSYSCALL to
avoid a default gate VMA to be created. However that default gate VMA
was removed entirely in commit a6c19dfe3994
("arm64,ia64,ppc,s390,sh,tile,um,x86,mm: remove default gate area").

Remove the now unnecessary conditional.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Reviewed-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Signed-off-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>