arm64: Treat the bitops index argument as an 'int'

The bitops prototype use an 'int' as the bit index type but the asm
implementation assume it to be a 'long'. Since the compiler does not
guarantee zeroing the upper 32-bits in a register when used as 'int',
change the bitops implementation accordingly.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>