x86/PCI: Add support for the Intel 82374EB/82374SB (ESC) PIRQ router

The Intel 82374EB/82374SB EISA System Component (ESC) devices implement 
PCI interrupt steering with a PIRQ router[1] in the form of four PIRQ 
Route Control registers, available in the port I/O space accessible 
indirectly via the index/data register pair at 0x22/0x23, located at 
indices 0x60/0x61/0x62/0x63 for the PIRQ0/1/2/3# lines respectively.  

The semantics is the same as with the PIIX router, however it is not 
clear if BIOSes use register indices or line numbers as the cookie to 
identify PCI interrupts in their routing tables and therefore support 
either scheme.

Accesses to the port I/O space concerned here need to be unlocked by 
writing the value of 0x0f to the ESC ID Register at index 0x02 
beforehand[2].  Do so then and then lock access after use for safety. 

This locking could possibly interfere with accesses to the Intel MP spec 
IMCR register, implemented by the 82374SB variant of the ESC only as the 
PCI/APIC Control Register at index 0x70[3], for which leaving access to 
the configuration space concerned unlocked may have been a requirement 
for the BIOS to remain compliant with the MP spec.  However we only poke 
at the IMCR register if the APIC mode is used, in which case the PIRQ 
router is not, so this arrangement is not going to interfere with IMCR 
access code.

The ESC is implemented as a part of the combined southbridge also made 
of 82375EB/82375SB PCI-EISA Bridge (PCEB) and does itself appear in the 
PCI configuration space.  Use the PCEB's device identification then for
determining the presence of the ESC.

References:

[1] "82374EB/82374SB EISA System Component (ESC)", Intel Corporation, 
    Order Number: 290476-004, March 1996, Section 3.1.12 
    "PIRQ[0:3]#--PIRQ Route Control Registers", pp. 44-45

[2] same, Section 3.1.1 "ESCID--ESC ID Register", p. 36

[3] same, Section 3.1.17 "PAC--PCI/APIC Control Register", p. 47

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.2.21.2107192023450.9461@angie.orcam.me.uk

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