ARM: lpc32xx: remove unused header file clock.h

The removed clock.h file is a leftover after moving the platform to a
common clock framework driver, it contains unused "struct clk"
definition, which under circumstances may coalesce with a generic
"struct clk" declaration for clock consumers. Also remove useless
include of the removed local file from a single source file
mach-lpc32xx/pm.c.

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