powerpc: Avoid bad relocations in iSeries code

powerpc: Avoid bad relocations in iSeries code

Subrata Modak reported that building a CONFIG_RELOCATABLE kernel with
CONFIG_ISERIES enabled gives the following warnings:

WARNING: 4 bad relocations
c00000000007216e R_PPC64_ADDR16_HIGHEST  __ksymtab+0x00000000009dcec8
c000000000072172 R_PPC64_ADDR16_HIGHER  __ksymtab+0x00000000009dcec8
c00000000007217a R_PPC64_ADDR16_HI  __ksymtab+0x00000000009dcec8
c00000000007217e R_PPC64_ADDR16_LO  __ksymtab+0x00000000009dcec8

The reason is that decrementer_iSeries_masked is using
LOAD_REG_IMMEDIATE to get the address of a kernel symbol, which
creates relocations that aren't handled by the kernel relocator code.

Instead of reading the tb_ticks_per_jiffy variable, we can just set
the decrementer to its maximum value (0x7fffffff) and that will work
just as well.  In fact timer_interrupt sets the decrementer to that
value initially anyway, and we are sure to get into timer_interrupt
once interrupts are reenabled because we store 1 to the decrementer
interrupt flag in the lppaca (LPPACADECRINT(r12) here).

Reported-by: Subrata Modak <subrata@linux.vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>