i2c-imc-skylake: apply LKML review fixes

Apply senior-review feedback to the driver, validated on hardware
(Skylake-X / X299). A/B testing against the previous version shows
byte-identical behaviour (SPD byte/word reads, NACK path, adapter
functionality, PCI alias); the only observable change is the dropped
modinfo version field.

  - Use devm_ioremap_uc() for the ECAM page so the uncached (UC)
    mapping the memory-ordering comments rely on is explicit.
  - Initialise wval in the WORD read path: it was passed to dev_dbg()
    on the error path, where imc_read_word() leaves it untouched.
  - Drop MODULE_VERSION() (discouraged for in-tree drivers).
  - Iterate over ARRAY_SIZE(s->adap) instead of the literal 2.
  - Name the config-space offsets (CFG_VENDOR_DEV, CFG_IMC_BUS).
  - Restrict Kconfig to X86_64 (Skylake-X is 64-bit only).
  - Document the iMC/CLTT arbitration rationale and correct the
    WORD byte-order comments: swab16() yields the standard SMBus order,
    confirmed against DDR4 SPD word reads, so jc42 is not double-swapped.

Signed-off-by: Simone Chifari <simone.chifari@gmail.com>

docs/submission/Kconfig.kernel

@@ -1,6 +1,6 @@
 config I2C_IMC_SKYLAKE
 	tristate "Intel Skylake-X iMC SMBus adapter"
-	depends on PCI && ACPI && X86
+	depends on PCI && ACPI && X86_64
 	help
 	  Say Y here if you want kernel support for the integrated memory
 	  controller (iMC) SMBus engine found in Intel Skylake-X / Cascade