ANDROID: fix BIT() redefinition

Commit fea30ad1 ("ANDROID: preserve CRC for some DRM functions")
caused the BIT() macro to be redefined because vdso/bits.h is included
through vdso/datapage.h in some other files.

Move the __GENKSYMS__ BIT() check to vdso/bits.h in order to fix this.

Fixes: fea30ad1 ("ANDROID: preserve CRC for some DRM functions")
Change-Id: I767d75e7e40b5acfa9b66754c7b2b74879a28de5
Signed-off-by: Michael Bestas <mkbestas@lineageos.org>