x86: Avoid magic number with ELCR register accesses

x86: Avoid magic number with ELCR register accesses

Define PIC_ELCR1 and PIC_ELCR2 macros for accesses to the ELCR registers
implemented by many chipsets in their embedded 8259A PIC cores, avoiding
magic numbers that are difficult to handle, and complementing the macros
we already have for registers originally defined with discrete 8259A PIC
implementations.  No functional change.

Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/alpine.DEB.2.21.2107200237300.9461@angie.orcam.me.uk