ARM: lpc32xx: remove leftovers of legacy clock source and provider drivers

After switching the platform to common clock framework there is no
more need to keep dead code in arch/arm/mach-lpc32xx, which glued
legacy clock source and clock provider drivers, remove the leftovers.

Acked-by: Sylvain Lemieux <slemieux.tyco@gmail.com>
Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>