x86: capitalize function call interrupts consistently

Impact: aestetic

Capitalize function call interrupts consistently.

All other descriptions in /proc/interrupts are capitalized except
for "function call interrupts". Capitalize it too for consistency.

While that's technically a published ABI I think the risk of anyone
relying on that text to stay the same is negligible.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>