rtl818x: change misleading names for few register bit definitions

In rtl8180/rtl8187 drivers, few register bit definitions have
names of form FOOBAR_SHIFT, suggesting they should be used as
shift offset, for example
reg |= (1 << ENABLE_FOO_SHIFT).

However they are actually defined as (1 << x) and thus they are
used (correctly) like
reg |= ENABLE_FOO_SHIFT;

This patch kills the misleading _SHIFT suffix.

Signed-off-by: andrea merello <andrea.merello@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>