ARM: hwcaps: use shifts instead of hardcoded constants

The HWCAP numbers are defined as constants, each one being a power of 2.
This has become slightly unwieldy now that we have reached 32k.

This patch changes the HWCAP defines to use (1 << n) instead of coding
the constant directly. The values remain unchanged.

Signed-off-by: Will Deacon <will.deacon@arm.com>