ARM: debug-ll: rework lpc32xx handling

LPC32xx can not yet be configured in a multiplatform kernel, but
if we ever get there, enabling one of the LPC32xx platforms
while trying to use DEBUG_LL for another platform can default to
the wrong UART address, as the options are purely based on the
architecture being enabled or not.

This changes the logic to use the LPC32xx default addresses only
if we have also picked the respective Kconfig symbols introduced
here.

While we're at it, this also reorders the virtual address as
it should be.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Vladimir Zapolskiy <vz@mleia.com>