sparc: compat: Allow including asm/compat.h for 32-bit

We have several files on sparc that include linux/compat.h and expect
asm/compat.h not to be included for 32-bit builds, otherwise we get a
build failure.

Since we need to include asm/compat.h for compat time_t handling on all
32-bit architectures now, this hides some portions of asm/compat.h in
order to let the rest of the file get included.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>