omap2 clock: add support for inverted enable bits

omap2 clock: add support for inverted enable bits

On 3430ES2 (and presumably beyond), some clock tree branches from
DPLL3 & 4 can be powered down by setting 'PWRDN' bits in CM_CLKEN_PLL.
It appears that an easy way to power these branches down in our
existing clock framework is to use the PWRDN bits as clock enable bits
for the specific DPLL branches they affect.  The problem with this is
that the meaning of a set PWRDN bit is 'disable,' not 'enable.'  So,
introduce a new clock flag, INVERT_ENABLE, that clears the bit on
'clock enable,' and sets the bit on 'clock disable.'  This flag is used
on all PWRDN clock branches in the 3430 clock framework.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>