arch: remove GENERIC_FIND_FIRST_BIT entirely

arch: remove GENERIC_FIND_FIRST_BIT entirely

In 5.12 cycle we enabled GENERIC_FIND_FIRST_BIT config option for ARM64
and MIPS. It increased performance and shrunk .text size; and so far
I didn't receive any negative feedback on the change.

https://lore.kernel.org/linux-arch/20210225135700.1381396[email protected]/

Now I think it's a good time to switch all architectures to use
find_{first,last}_bit() unconditionally, and so remove corresponding
config option.

The patch does't introduce functioal changes for arc, arm, arm64, mips,
m68k, s390 and x86, for other architectures I expect improvement both in
performance and .text size.

Signed-off-by: Yury Norov <[email protected]>
Tested-by: Alexander Lobakin <[email protected]> (mips)
Reviewed-by: Alexander Lobakin <[email protected]> (mips)
Reviewed-by: Andy Shevchenko <[email protected]>
Acked-by: Will Deacon <[email protected]>
Tested-by: Wolfram Sang <[email protected]>